understanding BMPs with alpha channels

Gimp 1.2.3 certainly doesn't: it loads the bitmap successfully, but only shows 3 channels (R, G and B).

Time to upgrade my Debian box to sarge, maybe?

Alternatively, I think I might cobble something together to separate the alpha channel out as a separate monochrome bitmap, and then recombine them after I've edited both (which I think I can do by telling PSP to load the separate bitmap as an alpha channel).