Doug, this has been mentioned many times already, but to summarize: OS2008, which runs on both the N800 and the N810, has built-in USB host functionality. Basically, all is needed is a USB cable with a male end that fits into the N8X0, with pins 4 and 5 soldered together, and a female end to which you can connect any other device. In the N800's case, all you need is a Mini-AB (M) to Type A (F) cable, then cut (some of the) shielding from the Mini-AB end so that it fits into the connector on the tablet. Then just connect your USB keyboard or pendrive and the tablet will recognise it. If you connect a pendrive, it will even open the file manager to show you the files on it!

HTH.

EDIT: Yes, it _will_ supply power, but is limited to a maximum current of about 125 mA IIRC.