Is this in the imp cave in the fjords, at the back? You can stand in the doorway (ie without getting into the fire) to clear out the other imps, but for the boss you need to enter the room and get a short cutscene before you can attack him.
Other than possibly taking fire damage, depending on your level and stats, etc, there shouldn't really be anything particularly troublesome about this fight. The usual suggestion apply (lower the difficulty level, use temporary stat/armour boost potions, summon your creature, come back at a higher level or with better equipment, etc).
What's the problem, exactly, and what build character are you playing?
