Thanks for the advice folks - I was with learning slowly earlier and we did not anticipate major surgery, just perhaps a bit of a boost for about £30 or £40, probably as you suggest above from ebay, but we could not find the cpu support list for his motherboard.
We already installed everest which told us the original information, and I have some memory with which he is going to perform his first upgrade.
To be honest with you the only upgrades worth doing with a PC this age are a larger hard drive and perhaps more memory depending on the price of the memory, upgrading the CPU presuming it will take a faster one means buying second hand as no one does processors this slow anymore.
This pc is learning slowly's first one and is so old that you are undoubtedly right.
We were just curious as to what it could be upgraded to, as if it was in the region of 800mhz it might be worth £15 on ebay.
Learning slowly only uses the pc for surfing at the moment, although he does have a cd writer to put his photo's on. We are working on a very limited budget, although some of the suggestions above are great value.