David,
When I was at my last job we solved the same problem using a combination of AbiWord/Ghostscript to perform .doc --> .pdf conversion. As several posters have mentioned, the difficult part is not .ps to .pdf - Ghostscript handles this nicely. Getting .docs into .ps is an utter nightmare, though. At our request, one of the developers of Abiword added a command-line "print-to-ps" function that works on *nix builds of Abiword - it's still there as far as I know.
In the end, we weren't particularly happy with Abiword import filters - they don't handle tables, among other things. Toward the end of my time there we were investigating OpenOffice as well:
http://api.openoffice.org/source/browse/api/odk/examples/java/DocumentConverter/
I've done pretty exhaustive research in this area, and basically you're limited to:
1) a windows box running a closed solution - activepdf is one of the better known players, but you can check out several on pdfzone.com
2) one of the hacks I mentioned above - I don't know of any better solutions running on *nix.
