A 'hard crash' or BSOD is usually the sign of overheating, but it could also be driver problems. A DXDIAG report (Start->Run->DXDIAG->Save all info->copy-and-paste info from dumped text to here) can go a long way to help point out any obvious problems, though...
I spotted a pretty good driver guide around here that could be of help, for a clean driver reinstall, and you can find find my comparable guided I posted
here. I don't know if a x1900 is any different, but ATI cards typically are picky with driver installs, and I would always do a clean reinstall. I wouldn't do the same with chipset drivers, though, as deleting them more often then not leaves you with an unbootable windows you need to fix up in the recovery console.
Edit: As far as gfx card cooling goes, I prefer artic cooling's accelero if you don't have a comparable one on already, plus some cheapie tape-on ramsinks. Other than that, try to cram a 80mm fan below your card for exhaust if you don't have many add-in cards, and if not get a decent sized slot-blower.