I am pretty sure that the gtx 2__ series cards were not supported in 10.5.x installations, which is why I held off until 10.6 was released to get osx86 running on my machine.

gtx260's load up just fine with a recent version of graphics enabler in your bootloader in 10.6. You should grab a retail DVD and upgrade!

I'm sorry, I have no advice as to whether or not they ever got gtx2__'s working in leopard, but when I looked around a lot a year-ish ago there was no solution.