Adobe Acrobat 5.0/Acobat Reader 8.0

A third question, still on EndNote X1.0.2.

I have Adobe Acrobat 5.0 on my system (for PDF creation), and Acrobat Reader 8.0 (for reading PDFs). Acrobat 5.0 was installed first, but the PDF file association in Windows Explorer is with Reader 8.0. However if I select the PDF link, Acrobat 5.0 opens every time, unless Reader 8.0 is already open. Is there any way I can get 8.0 to open every time?