Hey guys i have a presario 6000series

AMD athlonXP 1800 (1.53GHz)
512MB DDR
60GB UltraDMA HD
nVidia GeForce2 w/ 32MB allocated as Video Memory
running windowsXP

I have had the computer for about a year or so now and what do you guys think i can upgrade to make a little faster. I am guessing the GHz but i was wondering how fast i can go. Doesnt the motherboard matter on how fast i can take the Ghz ?