nVidia geForce 7600 GT dying in late '06 white iMac (?)

Hi everyone. Having some pretty serious video problems with the iMac I bought a few years ago (specs below). It has a nVidia 7600 GT in it.

I mainly use XP on Boot Camp for gaming. A couple of weeks ago, I noticed that the video would briefly become non-responsive, then kick back in, but not before ruining my progress in whatever game I was playing. It got progressively worse, until finally seizing the whole machine and displaying intermittent little lines & dots over whatever was on screen at the time. I would reboot, and move on with life, but the frequency of the issue increased over the next few days. I took a break from gaming, but continued using the iMac in OS X as it is my primary work computer as well. The other day, for the first time, I booted up and got the gray apple screen but when it usually turns pale blue then shows the Leopard login, it went totally black instead.

I tried booting into XP to see if maybe it was software related, but now I'm getting little blue lines & dots all over the Windows XP boot screen (the one with the little progress indicator at the bottom), until it finally gives me the blue screen of death.

So now, I can't boot into OS X at all. It begins to boot normally, but I can't get to the login screen. I've been banging my head against the desk looking for similar problems from others, but I can't find a solid answer.

My gut feeling is that the video card is fried, and I'm gonna have to spend a pretty penny to get it replaced.

Out of warranty, of course, and no AppleCare. I'm not even sure what my next step should be. Maybe the Genius Bar? I don't want to call and pay someone to tell me what I already suspect, and I certainly don't want to pay Apple for labor on a job I'm sure I can do myself.

Has anyone else had this problem with the 7600 GT? I really need to get this machine up and running again soon. I've got my MBP, but I miss my 24" display for design work....