Not only is calibre the one stop solution to all your e-book needs, you can use calibre to view or convert PDB files, it has a built-in ebook viewer that can display all the major ebook formats. It has full support for Table of Contents, bookmarks, CSS, a reference mode, printing, searching, copying, customizing the rendering via a user style sheet, embedded fonts, etc.
CBZ, CBR, CBC, EPUB, FB2, HTML, LIT,
LRF, MOBI, ODT, PDF, PRC, PDB,
PML, RB, RTF, TCR, TXT
The calibre e-book viewer can now view all the e-book formats that calibre can convert.
Calibre is freeware, available for Windows, Mac OS X and Linux.
Edit: maybe you can use the Palm OS Emulator to open the files.