A common request I receive is for links to MSMQ documentation. What I find is that people haven't looked at what's already available to them "out of the box", as the phrase goes. The Help that is shipped with Windows is comprehensive - even I don't know all of it - so don't worry about being able to find good content on the Internet.
A shortcut to the help on Windows 2003 is "%windir%\Help\msmqconcepts.chm"
I tried to find a way of creating a link to the local Windows 2008 file but gave up trying to get HelpPane.exe to load MSMQ.H1S.
Otherwise, click Start, click Help and Support, and then search for Message Queuing.
If you must have something online:
And there is always the Microsoft Message Queuing home page on Microsoft.com although it's in desperate need of a refresh.