It takes over7 min just to load up the internet...
my daughter is enjoying having her own computer but hates waiting for games and sites to load up!
Apart from a couple of remarks like the above, we don't really know how "slow" it is. Reading those things I wonder quite strongly if this computer is not "slow" because it is old, perhaps it is slow because something is wrong with it. For example if the hard drive is very nearly full, is beginning to fail, or is badly fragmented, or gone into PIO mode, then the machine would seem a little sluggish. If the wireless connection needed troubleshooting. But most of those points seem to have been covered. (Viruses?) Even an entry level machine from 2004 with only 512 MB of RAM should be reasonably brisk at web surfing (unless the connection is a particularly poor one). Especially if it has a newly installed XP. Modern games are another matter. There is a lot here that we do not know. However I would put 1 GB of RAM in it and format the disk and reinstall XP and all service packs and see how it worked after that. If it was still bad I would start thinking about alternatives. This thread could meander on for quite a few more pages. Best of all would be if someone technically knowledgeable and trustworthy (maybe a relative, family friend or local nerdy teen would give this machine a thorough hands-on going-over (a tune-up) and see if there is anything obvious that needed putting right. The trouble is, if that knowledge and fitting of RAM, CMOS battery etc has to be paid for at commercial rates, like from a repair store, then you are spending a good part of the cost of a new computer or a more recently made used one.
Less expensive than a new computer would be a "modernizing kit" which would be a cheapish budget new motherboard/cpu/RAM combo deal that would fit in the case and not tax the power supply unduly.