I have the same problem. The response to clicking on any url
hyperlink in outlook (2007, running on Vista Ultimate on a Dell Core
2 Duo desktop in my case) is a Warning dialog (yellow triangle and
exclamation mark) with the text:
"General failure. The URL was:
"
http://www.anysiteyoulike.com". The system cannot find the file
specified."
I am running Firefox as my default browser.