I had no trouble (apart from being a novice) in Saving As from GIMP
2.6 and importing that BMP into Inkscape.
(I'm using Ubuntu Studio 11.04.)

The catch may be, that the File Type option is "accessed by" a
triangle, where you might expect a drop-down list.

Moreover, I did expect some glitch when saving my image as BMP. It was
not present when saving to other formats.

I'm using U10.04 stock Gimp is version 2.6.11.
The file drop down menu has a save as selection. At the bottom left hand
corner left click on the arrow for Select File Type (By Extension). This
will give you access to saving as a BMP file. On my install the BMP
selection is seven entries from the bottom.

To verify if it's some sort of conflict between the mouse and tablet
try unplugging one of them and opening the 'Save As' dialogue again.
If it works correctly with either one of them plugged in alone then
that would confirm a conflict of signals.

Unplugged one, then the other. I still don't get the right open/save dialog. It
goes directly to a folder and you can't select a thing except by the keyboard at
times. Every other program will open the folder and I can select/change/rename
whatever. Gimp simply won't let me.

Could be a program error then so try going into Synaptic Package
Manager and searching for GIMP then right click and select 'Mark for
Complete Removal'. This will remove all traces of GIMP including
dependencies that aren't needed by anything else.

Then install GIMP again and see if the problem is fixed.

I found another manual to install the tablet. This one said to take Wacom Bamboo
pad out of the configuration. Now at least open works as it should. Save is
still weird. I can't save anything unless I retype in the file name again.
Normally I can just add a 2 or an a after the file name and resave. Not in Gimp.
Have to start from square 1.