Having been working with a pure "slate" style of computer for a while having a physical keyboard ever-present takes up a lot of space.
A Bluetooth keyboard and mouse back in the office go's a long way.

These people make a very nice onscreen keyboard
AssistiveWare - Assistive Technology Products.webloc

Also here are some places to check out

http://digitalww.com/121TSK.htm
http://www.magictouch.com/products.html
http://www.cybertouch.com/index.html

This is the new Troll Touch screen that if you wanted to play with you could probably get it to work

http://www.trolltouch.com/slipcover.html

Hope this helps
Joseph