For compatibility, go to <A HREF="http://www.ntcompatible.com" target="_new">http://www.ntcompatible.com</A>.
As far as a performance hit, under d3d, yes. It's a driver issue, not the OS. So as drivers (read:nvidia) are updated, things usually get better. If you're playing a 2d game, then no; there will be a performance gain.