Red Alert 3 crashes all the time

[Aanguish]

The title says it all. I recently bought Red Alert 3 off Steam, and for the first few Soviet missions, it was fine, then when I got to mission three, I started to get regular crashes to the desktop anywhere between 15 to 20 minutes into playing the game. It'd be a standard CTD, with a "RA3.exe has stopped working" error message. When I re-enter the game, the crashes start that much more quickly. This annoys me as I thought I'd fixed it just before posting this- I disabled my second screen, which seemed to make it last a lot longer before going down.

My specs:
Windows 7 Ultimate
Athlon 64X2 6000+ running at 3.1Ghz
Radeon HD 4870 with 1GB of RAM
4GB of RAM
E-MU 0202 USB audio interface
ASRock AM2NF6G-VSTA mainboard.

Please help, I absolutely love this game, which compounds it crashing all the time.

[McGoWaN]

Iv never had issues with crashing and i also have a 4870. im running an E8400.