Lots of great suggestions already...
Here are a couple of additional thoughts -
1) Spell selection: Buffs are great, but I would absolutely take invisibility. Using that in conjunction with Evilhalfling's outstanding fog cloud/ice sculpture idea is a great misdirection combo. It is also useful if the PCs have been spotted outside the lair. Cast invisibility, go for altitude, cast true strike, fly-by attack with jaw snatch on the softest looking target, fly away, breath, land and full attack until target is dead, rinse and repeat.
2) Lair prep: Most of the surfaces in the lair should be ice, honed to a fine, slippery sheen. On such a surface, unless the party has taken signficant precautions (such as ice cleats, etc) the party should be making rolls to stay on their feet any round they try to move more than half speed. The dragon might also keep semi-packed snow around the periphery of any large chamber to Bull Rush party members into, temporarily pinning them in the snow. A huge dragon takes up 15' feet of space, enough to get a couple of adventurers per Bull Rush. I think many DMs fail to use evironmental factors such as ice to the fullest extent. The dragon's icewalk ability gives it a huge tactical advantage in such a situation. Even if th party is using ice cleats, the cleats should probably slow their movement and/or prevent running.
I also agree with the large icicle deal - with a couple of improvements. Even with an INT of 12 (standard human intelligence with a +1 mod

), a dragon doesn't get to the "Old" age category without being crafty or lucky. The dragon does two further things to prep its lair. First, the major entry cavern has big icicles above, but the floor is designed so it won't hold the dragon's weight - but will permit creature of up to large size to walk on it without any problem. What's more, the ice floor covers a nice deep chasm. During combat, if the dragon lands on the floor (using a crush attack) or slams into the ceiling (dislodging a bunch of big icicicles to crash into the floor), the ice gives way and drops anyone in the area into the chasm for falling and crushing damage (from tumbling ice). An alternative would be to have them drop into an underground lake of frigid water (the dragon's bathtub) - the dragon follows up with a breath attack, freezing the water and immobilizing struggling/sinking PCs in ice
The dragon also has a "soft-spot" in the ceiling that it can escape through if things start to go bad. Of course, a huge dragon burrowing through the ceiling dislodges lots of ice that crashes down on the party or small avalanche that might temporarily bury them. This gives the dragon time to heal up, regain its breath weapon or start a large avalance to
really bury the PCs.
3) Allies: The dragon's proposition to local humanoids is simple - You scout for me, bring me the occasional captive to munch on, warn me of approaching danger and pay me some tribute and I won't eat you and your kids. I agree that a gnoll/winter wolf group makes nice minions. If the dragon has enough warning of the PCs approach, it definitely should hit them on the road, preferrably in the middle of a probing attack by the gnoll/wolf minions. It might be an invisible, fly-by, snatch and munch attack or just observing invisibly to gauge party strength and tactics.
My 2 coppers...
~ Old One