I'm not sure precisely what you are looking for as an answer - in general, some groups might be built with heavy ranged firepower and able to deal with the creature, while others won't be. In that case, they should seek cover to lure it lower - if there is no cover, and the DM goes out of his way to prevent creative solutions (such as letting it bite free of ropes with a minor action), then he is clearly just a bad DM, and out to kill the party.
But if a party does end up in an open field and has to fight him, then they have some options. Assume you only have one or two people suited to the fight - a ranger, maybe a wizard with long range spells. Others can still have some options. A rogue can use a crossbow at long range, or a longbow without proficiency (or with it, if elven). Any Str-based characters, such as Fighters and Warlords, and possibly Paladins and Clerics, can use Javelins at long range. Even a warlock can carry around a longbow and shoot for 20s.
If all the dragon does is blast them with Lightning Burst, then it is going to be a long, long fight - if they stay spread out so the dragon can only hit one target at a time, they fight is likely to go 40+ rounds. Depending on how well they keep alive their damage-dealers, depending on the dice rolls, I'd say it could go either way - the party has maybe a 50/50 shot of victory.
The key is, the dragon is doing just as piddling damage as the party. 1d6+4 damage a round? And the characters that will be the biggest threat to him - rangers, wizards, elven rogues - will be the hardest for him to hit... especially with a fighter who keeps marking him.
A party with a bow ranger, elven rogue, long-range wizard, strength fighter and strength cleric... is almost certain to win, in this environment.
A party with a halfling rogue, long-range wizard, strength fighter, wisdom cleric and warlock... is probably going to lose.
A party with a mix will have an even shot at it.
Now, if the dragon is willing to get close enough to use its breath weapon, the entire scenario changes. Its damage goes up significantly, cutting the party survival time down to 15-20 rounds. On the other hand, that means 1 in every 3 rounds, he has gotten within 10 squares of the party, which opens up many more powers for casters - potentially even ones that can bring him down to the ground where he can be cornered by a fighter.
Honestly, if the DM has removed all cover and prevented any creative solutions, than the party spreads out, takes out the ranged weapons every character should have bought back in town, and hopes for the best. That's basically all there is to it.