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.