You should be fine, a 9800GTX draws 13A from the 12V rail and that PSU can supply 16A per 12V Rail, a GT should draw less. Your total system load should be less than 300W with that CPU and graphics card. If your fans are powered off 12V make sure they are powered from the other rail on the PSU.
The smaller Cooler Master PSUs have historically been junk, I don't recommend it.
The PC Power & Cooling S75CF 750W is on a killer sale right now. It's bigger than what you need, but too good to pass up IMO. It is a little longer than most, but it should fit unless you have a small case.
Original Price: $249.99
You Save: $140.00
$109.99 ($69.99 after $40.00 Mail-In Rebate)
Well in my opinion I would think about upgrading the all system,
At the moment I run a AMD 6000+ CPU with a Asus crosshair motherboard with 1 Asus 8800GTX graphics card, and 2 raptor drives, and Im starting to find my system is really showing its age,
It just seems pointless now to just upgrading 1 hardware on my system,
So for instance if I was to put the most expensive graphics card onto my Motherboard, I think it would be just let down by the slow AMD 6000+ CPU.
Example if you were to get a relay team and enter them into the olympics and 1 of the 4 was a fatty !!, he would just slow the all team down,
That make sence !.
So I kind of look at my pc as a team of componets that need to be as good as each other and if I was to spend money on upgrading 1 component would it be worth it if that component was just finding its self to fast for the rest & been wasted.
But in ansewer to your question the Borg is right that graphics card is big, something like 11inch or 28cm long, and you will need to work out if your power supply on your pc can take it.