
Well all you can do is raise the RAM and core speeds bit by bit and then back off a couple of notches when glitches appear. It's worth trying RAM first and then core and vice versa to see if there's any diff. Some people have found diff utils help to achieve a higher o/c, haven't a clue how.

Anyway, o/c'ing your CPU is very unlikely to limit the gfx card's ability to o/c. The main reasons why this could happen are excess heat (poor case airflow/ventilation or raising voltages) or PCI/AGP clock speed running very far from the standard 33/66. You could try setting your CPU back to defaults and see if you get a little more from your gfx card, unless the game is very CPU dependent most of the CPU o/c will be wasted anyway. Not to knock the GF3 they are still very fine cards and not really worth upgrading from yet.