Here's an old, cheap, but possible tactic.
Send an advance scout/wizard. Send him in silenced and invisible, and flying. Maybe send everyone in that way.
Wizard should have lots of Silent
Rope Trick spells prepared and as much alchemist's fire as you can carry.
Fly/sneak around the lair. Find the dragon.
Cast the silenced rope trick spell up near the ceiling (and hope he doesn't notice the rope appear). Load up "dimensional pocket" with alchemist's fire or fighter-type. Pull up rope and "close" pocket.
Repeat until the area over the dragon is swamped with "booby traps". Wizard and other friends fly to "corner" of room. Set up (silenced) walls of force on five sides (DON'T FORGET BENEATH FEET plus top of box and three "sides" (leave yourself an "out").
Everyone holds their action (using telepathy to coordinate) so you all act on the same init count. Make sure you're all hasted, too.
ROUND 1: Archer types let fly with volleys. The "better counterspeller" Wizard does a targeted dispel on dragon with partial action from haste. Follow that up with the biggest, baddest area-effect spell you can think of. Other casters summon lots of creatures to interpose between you and dragon.
Everyone takes 5' step "into" wall-of-force safe haven, cutting off line-of-effect for physical, spell, and other attacks unless dragon takes more than a 5' step himself. Most importantly, AMF doesn't hurt Walls of Force. You don't expect to use them forever, just in the first round when you expect him to hit you with the biggest blast he's got.
ROUND 2: Everyone scrambles away from wall of force (as soon as he sees his breath and such "bounce off" he'll probably try to seal you in with a "sixth" wall - avoid letting that happen by scattering. At least once wizard should hit a pocket of rope tricks with an area dispel, bringing down "hidden fighters" and/or alchemist's fire on dragon. Use tactics as detailed in previous posts.
CHEESIEST OPTION I CAN THINK OF:
Use the twinked Combat Reflexes/Great Cleave/Summon Monsters trick - put your best-slugging fighter near dragon and summon tons of little wussy creatures behind him. Wussy creatures are commanded to move through fighter's threatened area and attack dragon. This triggers AoOs.
Fighter type takes AoO on creatures, and should bring them down (they are wimpy, after all - use a Summon Monster III to summon multiple creatures from Summon Monster I for instance). When this happens, Fighter uses Great Cleave to "follow through" into Dragon (one attack at highest BAB assuming dragon is adjacent to Fighter). This is technically allowed since the Great Cleave attack is NOT an AoO - it is a "free attack" and you are allowed to direct multiple uses of it at the same target.
Dragon could smack down on wussy-critters, too - but is limited to one AoO per round (most dragons don't have a Dex bonus so have no reason to take combat reflexes), so while he might get a single free hit on Fighter, the Fighter (with a buffed-up Dex - could have a Dex as high as 34 or so (18 plus 2 racial plus 3 points for advancement plus 5 from Cat's Grace plus +6 from Bracers of Dexterity) for a total of 12 AoOs per round.
That's right - using this tactic essentially gives your fighter 12 "free" attacks per round to the dragon's 1 "free" attack. That should help your odds CONSIDERABLY.
Even better if you can get this chain going with two fighters, with wizardly support for all the summoned cannon fodder... especially if they have a rogue level or two (or three - the BAB suffers no more with 3 levels of rogue than 1 and a third level of rogue adds more sneak attack damage AND adds uncanny dodge at an average cost of 6 hp).
With even one AoO-twinked fighter, you have a shot. If your "new" 14th-level character is designed with this in mind (might be good to use a halfling with their racial Dex bonus - for the extra AC and attack point due to size, even with the loss of a strength point, is probably preferable to the elf with a loss of 14 hp (one per level) due to Con penalty).
A halfling ftr11/rog3 twinked for AoOs:
Dex 34 (as explained above) for a +12 modifier
Str 27 (16 plus 5 from Bull's Strength plus 6 from Girdle of Giant Strength) for a +8 modifier (+12 when using a weapon two-handed)
BAB: +13
Feats: Combat Reflexes, Power Attack, Cleave, Great Cleave, Weapon Focus (longsword; wields two-handed), Weapon Specialization (longsword; wields two-handed) - these can all be picked up as bonus fighter feats and the character still has the usual 5 from character levels to play with...
Give him a flaming burst longsword - and if you can get a dragonbane sword, so much the better. For ease of use, let's assume that he has a +4 "base" weapon (since a GMW will grant this anyway).
Total bonus to hit: +31 (+13 BAB, +12 Str, +4 magic, +1 size, +1 weapon focus)
Use of bless or prayer could add an additional +1 and if the dragon is flanked, that's another +2 circumstance. If you fly him in so he is attacking from above the dragon, you get another +1 circumstance (circumstance bonuses stack) so another potential +4 right there.
But assuming a "mere" +31 to hit, you'll score a hit on AC 40 with a roll of 9 or above (60%) of the time.
So with twelve attacks thanks to dropping your enemies in AoOs, you're looking at an average of (being conservative) seven hits on AC 40. That's a total of:
7d8 (sword) - average of 31.5
plus
7d6 (flaming) - average of 24.5
plus
84 (strength)
plus
14 (weapon specialization)
or an average of, let's see... 154 points per round with AVERAGE die rolls and no criticals (of which you're likely to see at least one)
If you catch the dragon flat-footed or flanked (much easier), you probably hit with one more attack AND you get your sneak attack bonus... that's a mere:
8d8 (sword) - average of 36
plus
8d6 (flaming) - average of 27
plus
96 (strength)
plus
16 (weapon spec)
plus
16d6 (sneak attack) - average of 56 points
In this case you do a paltry 231 points of damage per round... on average and with no criticals.
The idea is to try to bring this bad boy down in a single round, and this is the best way I can think of to do it... doesn't rely at all on SR.
Now, imagine this with TWO such characters flanking the dragon.
I'm sure there will be suggestions on twinking this character even further... but you get the idea, I hope. Figure out a way to crush the dragon with physical attacks in a single round - because that's all you're likely to get. Figure out a way to maximize a character for AoOs on wimpy targets; then set the rest of the party up to just "feed" the character gratuitous Great Cleave "shots" thanks to those AoOs.
Note also that the above is just trying to overwhelm the Dragon with a plethora of die rolls to bring the law of averages into play. You don't want to pin your hopes on a single lucky die roll.
--The Sigil