I have a nvidia FX 5900 Ultra running on gentoo linux and at idle its at about 60C, after playing games I top at about 80C(usally). If your worried about the heat make sure the room is cool, not hot. Also make sure the air flow in your case is good, since its a compaq I doubt you have much control over that. As a last resort you could try to replace the cooling on the card(voids warrenty). Anyway I would make sure its not something else, I know on linux X will lock because of this error
which I have heard some Win/BSD/Mac users have but in a different form. If you can try putting the card in another machine and/or putting another card in your current machine.