What is exactly the model of 9800GT? Is it the one without 6pin power connector?
Looking at the specs, it has 20A on 12V(1) and 18A on 12V(2) rails, so it's good PSU if that specs are true.
But again, IF the specs are true then you can use a single 9800GT (with OR without 6pin power connector) on that PSU.
Ah, I guess that 9800GT need 1x 6pin power connector from PSU.
How old your PSU?
The specs of PSU are good, but it only has 430W max. So, I think you will better with a brand new PSU, it also good for longer term. Get a trusted brand like Corsair, Antec, Seasonic, OCZ, SilverStone with 500W minimum for a single graphic card.
But if you are really just want to buy that 9800GT then 450W is enough for your need.