Hrm... well the Socket775 won't be any problem in general. I have a 775 with a PCIe card and did a fresh install when I upgraded to this. However my mobo came with a CD-ROM with drivers, and during the installation (I can't recall where/when) I was able to put this in and it installed any other stuff it needed.
If you're blue-screening off the bat, I might think something's wrong with the copy you have. I've heard some folks say that can happen (bad CD, just get another and it works, for example).
I don't have that much experience in the BSD area, so I'm afraid I'm of no help here.