Video problems

I'm having a problem artifacts that are all over the screen. Before trying a clean install I had lots and lots of glitches, specially in Safari, and it was causing the whole screen and computer to freeze. Now I see a lot of sparkles in all colors, even if it's a white-gray, light blue or black screen. The weird thing here is, when the darker blue screen appears it has no "sparkles" at all! They look like dead pixels even, but this is not the case.

Due to this problem I can't install any OS, I have a partitioned disk, and the smaller part has a clone of 10.6 install DVD though it won't work since it's hardware specific, from my other iMac. Still this disk is the one that helped me get into disk utilities, make the disk partition and copy the install disc there to avoid lags and errors from DVD loading.

I've gotten a few times, after lots of tries, to the language selection screen though the background or the dialog window itself are all corrupted, weird patterns, noise here and there, parts of background mixed up bottom with top, diagonal slices of color crossing the scree, a whole mess. Can go on a few steps and then nothing, freeze.

I've come to the conclusion I need a new GPU, I've tried every trick in this page and hundreds others. I found another case similar to mine here:

http://forums.macrumors.com/showthread.p...

Also, would any 7600 gt ddr3 256mb sdram works here? I mean, does it have to be nVidia or can I look for another brand?

Thanks.