You can get a 1Gig Memory on a Video card the XFX 7950GX2.
The Aero compatability is only a guideline I guess, I tried it with an XFX6800 with 256Mb Mem, Athlon64 3500 and it still runs kinda slow, oh and the GPU temp skyrockets as well.
If it doesn’t work, jam a screwdriver in there and jiggle it about.