And where do you propose he put it? In his socket 478 motherboard? Whatever.
Anyways, I agree with other posts in this thread, get some more RAM and get it in pairs to run it in dual channel. I would go with 512MB(2x256) or 1GB(2x512).
The reason you might not have noticed a speed difference is that maybe on your old setup you were running something other than XP. XP takes more resources than other operating systems.