People have put dual slot graphics card in the SN25P before, though there were times where some modding was needed. And no, the pci-e 1x will be blocked since the graphics card would be taking up two slots
And ryanv12, the 7800GTX is roughly equivalent to 2 - 6800GT SLIed and in some games, even 2 - 6800 Ultras
Ald