Actually, now I think there's a loophole to allow you to read Palm Doc files on a BlackBerry.

EDIT: Try the JEDI reader:
http://www.beiks.net/DShowTitle.asp?TID=24
It's a J2ME/MIDP eBook reader for java phones.

J2ME/MIDP midlet software works on BlackBerries, you can actually use Motorola/Nokia/Sony/Siemens java phone apps on a BlackBerry! more info.