well it depends if you can use dual channe then get 2x512 but if you cant be better off with 1stick of 1gig and also the cas latency tends to be higher on a tick wit higher capacity here's an example 512 corsair ram cas 2.5 or 1 gig corsair ram cas3
Indeed. Go for 2x512mb. You will have 2 empty DIMM slots to upgrade to a total of 2GB in the future, you'll also be able to use Dual Channel and there's also the latency issue. Also, it's worth to take a look at something other than ValueRam.