1. get a 512 stick to add to the one you have.
2. make sure it is the exact same type ie ...pc3200 with the same "latency timings"
3. the exact same brand would be nice but not critical
finally you'll be running in what they call
dual channel mode.... read up on
how to install the new 512 stick in
your particular motherboard (which slot to put the new stick in )*
dual channel mode runs very well, it would be my preference over one stick at 1 gig.........
it is very EASY to add or change ram, ground yourself before sticking hands in the case and make sure that your power cord is unplugged from the rear of your case before changing the ram.
you will really like the bump in speed going to 1 gig !!!!