Free but you have to register with the jedec site to get to the downloads.
Actually, direct links to the pdfs work just fine. Just use Google ;-)
The mfg datasheets and app notes for the ram chips on your DIMM may also help you understand what you need to do to make the ram talk.
You can use any other manufacturer's datasheets too, all DDR chips are (supposedly) compatible (within the bounds of the JEDEC spec -- there can be different timings, etc.)
Good luck.
Well at least for DDR-I only luck is needed, no divine intervention required like with DDR-II :-)
Segher