It says it has an PIII500 Coppermine.
I was able to upgrade a Presario 12XL401 from the Celeron 700 (10.5x66) that was in it to a PIII933 (7x133) Coppermine. Hopefully it's a Socket370 and not a microPGA. Either way, you should be able to upgrade. I can't find any documentation that says if it's microPGA. Use something like
CPU-Z and tell us what processor you have.
It looks like your's has a BX chipset, I think it'll only handle a 100MHz FSB CPU is all.