In this case UAC probably isn't going to cut it. You'll probably have to set up a group policy locally.
In windows do Start-Run and type in
gpedit.msc
Go to User Configuration -> Administrative Templates
From there you can go through and lock down whatever you want. It requires time to sort through but there are some online guides that will point you to some common options. Just look for "Group Policy".
Just an FYI from an admin, usually the options are "Not Configured" , "Enabled", "Disabled". DO NOT ASSUME what these functions do. There are lots of bizarre double negative and just plain ambiguous settings. Test to make sure whatever setting you do, does what you think it should. Try it in a VirtualBox first and play around with the settings to get something that fits your needs. Also keep an Administrative account on the computer so you can log in and change settings, or help them install something. As an additional plus, try to install the free version of LogMeIn. I find this tool to be invaluable in troubleshooting my parents computer remotely. It'll save you a road trip to do some basic help desk stuff.
Hope this helps
Forgot there's another way to probably get what you want.
http://jaredheinrichs.com/how-to-turn-a-wi...to-a-kiosk.html
Basically use the Group Policy and make it so they can only launch iexplore.exe or firefox.exe
Add mmc.exe so you can log in and edit the group policy in case you need to do anything.