Wow, your custom title kinda says it all.

Anyway...modern games, like the system blowing ones (Doom 3, Farcry), can and likely will use up all that RAM, especially if you have other programs running in the background, which you likely do. And since you got BSoDed, I'm guessing you're running 98 or pre-XP, in which case it's no big deal. 98 is screwy like that.