A while back, I looked around the internet for a simple one button mouse that my 3 year old could use to play the games on PBSKids.org. I was surprised that there was no cheap mice like this available. My kid was young and having a hard time clicking only the left mouse button, so I decided to write a small program that would allow me to easily switch so that all the mouse buttons functioned as the left mouse button.
Now I simply fire up one exe and then I can launch IE in kiosk mode (via "c:\Program Files\Internet Explorer\iexplore.exe" -k http://www.pbskids.org ) and I can walk away and let my kids have relatively safe fun playing games on the computer.
Here is a link to the program: SingleButtonMouse.exe
When run, it will automatically go into single button mode and add a notification icon to your task bar (click on this to toggle back to multi button mode). It has been tested to work in Windows 2000, XP, and 2008. (It should work in Vista too.)
For those interested, the source code is available here. It is written in C# (requires .Net 2.0 runtime) and uses windows api hooking.