MSDN Video demonstrating MSMQ 5.0 and SHA-2 incompatibility
Just noticed that MSMQ is featured on Microsoft Showcase as part of the "Windows 7 - Known Incompatibilites" series.
This 8 minute video, voiced by Nancy Strickland, covers the changes to the default hash algorithm used by MSMQ and what that means for sending messages between systems running different operating systems. There's a demo on how to edit the registry to change the defaults.
Note that the video quality is pretty poor - I tried this on three different machines just to check - but the audio is clear. So don't try to watch the video without audio as reading the slides, and especially following the registry editing demo, will be hard work.