I've posted this elsewhere as a reply, but I thought I'd let everyone know about it upfront as well.
You can use DocReader to convert ANY type of file into a mobi-readable format. Simply open your .pdf, .html, .doc, etc. file. Then select all of the text and choose 'copy'. Open up "notepad" and paste the text into it and save the file. Then, open up DocReader, change the file type to "text" and choose the file you just saved. Finally choose file/save as (this time leave the format as .pdb), and save your new mobi file.
After that, simply connect your BB to your PC via the USB cable, drag your .pdb into the mobi window, hit send, and voila...instant literary goodness! :D
DocReader can be found here, among other places: Mike Pickering's Website - DocReader
Hope this helps some people...I've been using this for years on my Palm, and it works just as well on the BB.