The PCI-e slot on these ASrock boards are physically 16x slots that run at 4x in terms of bandwidth.
Yes, that is what was trying to say, although not very clearly. I assumed that the card had to have 16x bandwidth available, but this is obviously not the case, as your link to the Asrock site shows.
Sorry to the OP for any confusion caused.
As for going for an 8800GTS, it would be a good idea if he was thinking of upgrading his Mobo+CPU some time soon, otherwise it will be wasted on his current system. It will be massively CPU bottlenecked, not to mention only having 4x PCI-E bandwidth available.