I don't think Tahoma ever was distributed as a bitmap font. The idea that it was likely came from this interview with Matthew Carter, Georgia & Verdana - typefaces for the screen - www.will-harris.com:
So instead of starting with outlines and then working to hint them for the screen, I started by simply making bitmap fonts. No outlines, just bitmaps.
Bitmaps are relatively easy to make and they show exactly how the fonts will look on-screen. This allowed us to make decisions about sizes, weights, and distinctions between serif, sans, roman, italic, all viewed in context. Working this way we came up with a definition for a certain number of critical sizes and weights.
Once the key bitmaps were done, I very carefully wrapped an outline around them. …
Carter — one of the preeminent contemporary type designers — didn't even pass the bitmaps to the person doing the hinting. The stress on the bitmaps in the interview was to support the idea that Tahoma was designed for the screen rather than the page.
As for making bitmap strikes,
otf2bdf from the FreeType project will do a decent job. Fontforge is a difficult program with a near-vertical learning curve, sadly.