New vid card, new problems, can you help me out?

Well, I just got this video card for only $50 and it seems great! The only problem is that now Minecraft keeps running out of memory, and sometimes Windows defaults to the basic theme then switches back. All drivers are updated and all settings are default, so what’s going on? I have 3.5 gigs of ram on the C itself so I can’t be running out.

I do have an ATI video card in the second slot but it’s working fine alongside the massive one taking up all the free space in my PC XD