I'm always happy to see more options for document format conversion. Today PDA24/7 is reporting about Makedoc, an online document conversion utility. It converts your text files to palmdoc (pdb) files.

[Edit] And some more conversion utilities are available here.

Proceed with caution, of course, as you would with any unknown source of software that you run. This might be a mainstream software provider, but I'm not personally familiar with them.