I think the palm OS (at least the classic version) can only handle special palm database files (the .prc and .pdb files) in its memory so the epub would either have to be modified, or read from external storage. But if you have Internet access you could read your epubs through the
bookworm site, although I don't know if you'd want to upload commercially purchased ebooks there.
I've just been taking my DRM-free epubs and converting them to mobipocket, and if I have the time, converting them by hand to the eReader format. (I like the eReader software better!)