There are lots of very informed threads about keyboards here at this forum, just use the search function. It's all been explained and detailed really.

@Gilbert:
When an external keyboard is in use there's no on-screen keyboard (except for a bug in the microb browser, now fixed I believe).

The HID keyboards are usually easier to set up, as they interface directly with the N800 out of the box. Example: Stowaway keyboards. The serial keyboards usually need an extra driver and setup, provided by an ITT member (link can be found as soon as you start searching for those threads). Example: Freedom keyboards.