Do you know what power supply you have?
The MS-7301 motherboard does have a spare PCI-E X16 slot for a graphics card upgrade, however I see this is a small form factor board.
Do you have enough ventilation for a higher performance graphics card?
And what do you do that necessitates such a high performance card? I.e. what games do you play?
You might not need an 8800GTS.