One thing you can do to save him some boot time and possible aggravation...
Win2k is a networking OS. As such it is set up to use logins and passwords.
When you get him all set up, go into the Control Panel and double click on Users and Passwords. Set yourself up as an Administrator as part of the Administrators Group. Just in case you need to do some Admin work on his box some day.
Once you've done this then click on his username and uncheck the box that says "Use login and password" or something like that.
This will take away the login function at boot up which can be a pain in the ass for a home user.
I set my wife's laptop up with Win2k just because it is so stable and the poor dear has too many other things to worry about during the day. She doesn't need her laptop going all ferklempt when all she wants to do is play some Scrabble.
Good luck!
I just hope that old Gateway will work with W2K.