OH!
I get your problem!
let me take a look at your dxdiag, if I can't figure it out I'm sure someone who knows more about this stuff than me will.
Ok, well everything seems fine.
I would suggest to try clearing some background programs while running the game since you only have 500mb of RAM, so close stuff like MSN, Xfire and such if you can.
It might also be your crapped out card that just instantly crashes when joining a certain map, or a certain game with a certain amount of bricks.
For that I suggest you try lowering everything to low in the options menu, and in the advanced menu be sure your Anisotropy is at 0
I don't suggest you try changing anything else, just wait until Badspot posts if this doesn't work.