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!!
The RAM upgrades are limited, although you can have 2gb ddr2 memory with 667mhz un-buffured 1.5v
I currently have 2gb (Corsair and Kingston) on the same system. 1.5gb is not supported (tried and not working)