I was tired of converting all my HTML ebooks to rtf, then to pdb using Palm Doc Converter only to lose all the nice touches like bold, italics and headings. Since there didn't seem to be a HTML to PML converter for OS X, I wrote one to get more practice in python.
html2pml.py will convert basic HTML file to a PML file suitable for use with DropBook to be converted into a proper Palm ebook. I must stress the basic part - it only does stylistic conversions at the moment. I have no need for tables or links, so I didn't write them in. It does however do what I want - preserve bold and italic attributes, headings, and also translates some non-ascii characters into PML Extended Character Set, and to plain ascii where not possible.
This small python script is released under GPLv2, license is attached. If you find it useful, need more features, or have comments/suggestions, let me know!