The answer to the OP's question is yes - it can handle two if you don't have like 6 hard drives.
But it sounds like the OP is considering buying a second 9800GT, in which case, I strongly recommend buying an HD4870 instead. They smoke 9800GTs.
It is, BY FAR, much better than Vista. This coming from an XP buff since 2004. Windows 7 runs worlds faster and better then XP on my gaming rig.
Who PAYS for an OS these days anyway?
Project Pat - "That Drank"
Three Six Mafia - "Where Is Da Bud?"
Killa Kyleon (feat Slim Thug) - "Badge on my Neck"
Daz Dillinger (feat Kurupt) - "My System"
Lil Jon - "BME Click"
to name a few.