honestly your better off installing a fresh version of 6.5. Some 6.0 version used splatt forums and some used toms bbtonuke forums, and still others used phpbb. So getting the right upgrade is the key factor.
6.5 is easy to install, download it from phpnuke.org and then get the installer here http://nukecops.com/downloads-cat-1.html
another thing you might want to download is the analyzer, it will check to make sure you have DB connectivity, it will also let you know if there are any security holes in your code. you can get it here
http://nukecops.com/downloads-file-13-deta...s-Analyzer.html