Here is a * free * (donations accepted) program that comes in handy when you want to give your little one a chance to hammer around on your computer without having the ability to break anything (software wise).

Programmer and Dad Scott Hanselman wrote this program to let his 2 year and 5 month old play on his PC. 

As babies smash on the keyboard, colored shapes, letters and numbers appear on the screen. Baby Smash will lock out the Windows Key, as well as Ctrl-Esc and Alt-Tab so your baby can’t get out of the application. Pressing ALT-F4 will exit the application and Shift-Ctrl-Alt-O brings up the options dialog.

Click on the picture to download: