Here are three models that your motherboard might be. Is your computer an Emachine, an HP, or something else?
I think you may have a Trigem Anaheim 2 or 2A motherboard. If I am right, you are maxed out at 600. The Anaheim 2 or 2A is a micro ATX (MATX) motherboard. Any increase in speed of processor will have to include a new MATX Motherboard. Sorry.
If your motherboard is a Trigem Cognac you can go up to a 1.1 Ghz Celeron FC-PGA with 128k cache(not FC-PGA2).
If it's a Trigem Anaheim 3 you can use a 1.0 Ghz P3 with a 133 FSB (this would be my recommendation), or a Celeron 1.1 FC-PGA with 128k cache (not FC-PGA2).
Here is a site that lists several models of Trigem boards including possible upgrades:
http://www.e4all.info/motherboard.htm
If your computer is an Emachine just look for the model number, if it is another maker, maybe you can tell by the description or find a nameplate on the board.
Good luck.