All you need do is install the mobipocket 6.0 beta on your PC. Follow the instructions and link your BB to your pc via the USB cable, and it will install it automatically.
As far as formats, ANY format is possible as long as you do a bit of converting first. I've been using a program called DocReader for years on my palm that takes any .txt file and coverts it into a mobipocket-readable .pdb file. Therefore, you can take an .html, .pdf, .doc or any other file, select all the text and save it onto your notepad as a .txt file. Once that's done, start up DocReader and convert to .pdb, then drag that into your mobipocket window...hit send, and voila...instant literary goodness through your USB cable. You can find DocReader here:
Mike Pickering's Website - DocReader