Quote:I'm also no computer whiz (jeez, why am I answering here?:P) but it seems like in most cases it's recommended that the RAM matches. So, having a 1GB RAM stick in one slot and a 256 MB RAM stick in another might cause some problems (computer knowledgeable folks please correct if necessary). So, you might opt to go just for one, 1GB stick with the option to add another at some point, or 2X500 MB.
Having matched sticks of RAM is necessary when running RAM in dual-channel mode, which that motherboard does not seem to support. You are right with the RAM type though.
A single stick of 1GB DDR2 667 is probably your best bet. It will allow you to upgrade to 2GB at some point if you feel the need (which is the maximum amount that your motherboard will support).
Another option for upgrading is to ditch that god-awful integrated graphics. Your motherboard has an open PCI Express X16 slot, so use it. Something like a Radeon X1600 or GeForce 7600GS will be a significant upgrade over what you have, and at very little cost (less than$100 USD).