A computer which will: Surf the Net: Process Words: Play Solitaire: should be more than possible.
If you want Windows XP, the ability to play Games of almost any kind and anything more than absolute basics, he will need to be imaginative.
So buy/borrow a 2nd hand monitor and speakers from someone who has upgraded.
Then all that is needed is the main unit. So go for a Celeron processor and Windows 98se and you should just be able to make it.
The trouble is that all software just adds to the price,