Oh, ok yeah. I thought it was web-based. Definitely a plain user account would work.
You can control so many aspects of this that it is hard to put it all in writing. Anything from deleting shortcuts (only works if he is lazy), to limited users and folder permissions.
Check this out (ignore sharing, just permissions)
How to Share and Set Permissions for Folders and Files Using Windows XP
And this
File and Folder Permissions
Microsoft articles can be rather boring, but they are often full of useful info.
Basically, whatever you do not want him to have access to, add his user account in the security tab and set the deny permissions. I would not do this to the whole program files folder, for instance, or he will probably not be able to load his profile properly.
Additionally, he will not be able to install many things, so he probably won't be able to put the game he wants on the machine to begin with.