There are a number out there that a free, and good. Two of my favourite for Windows are Bullzip (which works well on Vista), and Docudesk – which I’ve seen work well on XP, but I’ve not tried in Windows Vista as yet.
I like that Bullzip does password protection for PDFs – which is something that I need for my job.
If I need to stitch multiple PDF files together, or split a PDF file, I use PDFSAM (short for PDF Split And Merge), which again works well on Vista.
All these are free!