Yes, you can upgrade the memory as long as you do not have the system already maxed out. As mentioned in the above post, you can upgrade upto 2GB. It has 2 slots and max per slot is 1GB. The following link should help you find the right memory for your desktop. http://www.memorystock.com/memory/Compaqdx2200.html
If you need anymore info let me know. Hope everything works out as you 've planned. Cheers!!