New Compy Crashes SL mercilessly

i have a brand new machine, pentium d, 1 gig ram, radeon sapphire ati 1650. It SHOULD handle all my programs, such as all Half Life products and most importantly SECOND LIFE. I know this isn't a direct and true sl question, but after updating all my drivers, and getting directx, i have NO CLUE how to address this. I can survive in sl (omg TOTALLY lag free, too) for up to 10 minutes, tho its usually 3-5 min before i crash.
I'm at a loss, and careening onto hot frustration, lol. Please help if you can. Post here- or try IM me in SL- Fabala Snakeankle- i'll be signing in and out and in and out all day i think :/

Youre not on win vista right?

Brand new machine? Might it have some virus protection that is interferring with the cache? Or perhaps some vendor-supplied disk checker or software checking for updates that is constantly stealing focus/cycles from SL?