ASUS GeForce 9800GT OC'ing

How much are you overclocking it? If it's around 50 MHz or less you won't see any real upgrades in performance. You'd need to push it higher to do so. If the o/c software's not working then try MSI Afterburner.

^ agree with Lmeow.
Also, it depends on the other specs as well...

CPU? RAM? What resolution?

Windows Vista SP1
AMD Athlon 640 Regor 2.8Ghz OCed to 3.1GHz
2MB DDR2 667 RAM
ASRock 580 something motherboard
250GB WD HDD

The resolution varies depending on the game Im playing. Not sure onthe resolution Im running in ARMA 2 but its 1280Xsomething. When I put the sliders in the program where I want them I just dont notice much perfromance gain. Im just wondering if the Software is actually overclocking the card. How can I tell?

While benchmarking or playing a game, run GPU-Z and it will tell you the current clock & memory speeds, if it is what you set it to while the benchmark or game is running then the overclock is applied.