Just to add a couple things to Rob's post:
I have the Motion Computing TabletPC. I got the CD/DVD drive, the dock,
and the keyboard. In my office I dock it and use it as a desktop PC (the
Tablet itself acts as the monitor). At home I either put it on its
plastic stand and attach the keyboard, or just use it as a Tablet. Out
of the office I just use it as Tablet. Unless you are really a mouse
fanatic, I wouldn't recommend a mouse--I find the stylus to be much more
useful and natural.
Have you seen John Murch's and Jeff Frolik's info on TabletPCs?