Before you do anything, if it's speed you want, try putting a bigger RAM stick in: try
http://www.computermemoryupgrade.net
/types-of-computer-memory-common-uses.html
which will give you advice and info
I upgraded mine (2.9gb) from 256mb RAM to 1gb and the difference is amazing. Keep the same specs: in other words, make sure your RAM is ECC or non-ECC and has a similar PC no. eg PC2100, before you change. To find this out, download Belarc Adviser which is free and gives you all the info on your existing kit.