I've installed Adobe Reader X. The PDF file type was not automatically associated with Adobe Reader. So, I went through the standard process of adding it to the Windows Registered file types. It does not remain in the list. I've checked the box to "Always use the selected program.....", but when I reopen the Registered File types window, PDF is not there. PDFX is there and registered to open with Adobe Reader, but not PDF.
I forgot to mention, I'm running Windows XP SP3.