>I am running XP, so if I increase my memory from 256 to >512, I should see a big difference in my internet speed.
Well if you are running XP you should be on at least 512Mb anyway.
But as I said in my second append, more memory will probably not increase your download speed.
Your download speed is controlled by a number of network things (broadband speed, how busy the internet is, your network card etc) but will not change much even if you increase your PC memory.
But you should do it anyway, to speed XP up.