You need a few things:
You need a USB to serial adapter. I have an el cheapo based upon the FTDI chipset but almost any one should be supported.
You need a way to connect the USB to serial adapter to the usb port on the N800. I used a double female USB A adapter plus the standard USB cable that came with the N800. There are USB mini B male to USB A female adapters that would work too. If you are handy and willing to make your own cables you can just splice a mini B male onto a USB to serial adapter.
You need the kernel modules linked to from this thread and you need your tablet to be root enabled.
Get a root prompt, insmod the kernel modules mentioned above, place the N800 in USB host mode with the instructions on the wiki of this website, and plug in your USB to serial adapter. You'll get an error about USB device not supported and you will get another error about a file system not found, ignore them. Then all you need is a terminal program which I provided a link to but it seems not to work for bluehash.

Bluehash: OS2007 or OS2008? I think we must be running different versions of the operating system because I have no /dev/rfcomm entries.

David

Y