Re: Unable to install linux after insertion of xfx gts 250 512 mb
You could run memtest86+ from a livecd to prove to the kernel bugzilla people that your memory is ok. It would also be interesting if even memtest86+ won't boot.
Also, try removing the new card temporarily and retest with your hardware the way it was when it worked.
I once damaged a motherboard installing a new power supply. Its possible that you damaged your RAM or motherboard while installing the new video card. My suggestion would rule this out. BTW: You said Windows still works, but has it remained stable?