Have a look at my Guide on how to find out what hardware you have that is in my sig.
Use my steps there to find out what speed of RAM your computer has (ie: PC3200, PC2700, PC2100).
Regardless, it wont be higher than PC3200. Often, PC3200 is easier to find and sometimes cheaper than slower RAM. PC3200 will work on most any system that uses PC2700 or PC2100 RAM, but not vise versa.