I reckon you're going to waste hours trying to find what's causing it,so here's 5 options:
1. Install a PS Printer driver printing to the port FILE: Print your PM publication to this port and use Distiller to create the PDF from resutling outputted *.PS file. (Any hyperlinks in your publication wil be lost.)
2. Uninstall Visual Manufacturing. (Did you create a restore before installing it?)
3. PM6.5 isn't supported on WinXP. Install PM6.5 on Win2K or Win98SE. See here: http://kb2.adobe.com/cps/328/328682.html
4. Use your PM Licence number to move to InDesign while the generous discounts are still available. This is the best long term option
5. Spend £100 or so upgrading to PM7 (with no guarantees that the clash with Visual Manufacturing is resolved).
Thank you so much for all of the useful information!