MSN Messenger 6.0 installed; Outlook+Hotmail broken elsewhere

After installing & running MSN Messenger 6.0 on one
computer, another computer is now unable to access
Hotmail from Outlook. It simply prompts for the passport
credentials over & over. I can still access hotmail
directly via a browser, so I know the account & password
are valid.

The machine running Outlook [2002 (10.4712.4219) SP-2]
only has Windows Messenger 4.7.2009 installed. It is
still able to access all other mail accounts I use it for.