Message Owl can be added to any installation of Eclipse 3.5 that already contains the Web Tools Platform. If you are starting from scratch, the easiest approach is to download the Eclipse IDE for Java EE Developers - it contains everything you will need, plus a lot more besides.
Message Owl is distributed as a p2 update site and is easily installed using the Eclipse Help > Install New Software action.
Message Owl was previously part of the FUSE Integration Designer product, which has ceased development. Original authors are sgupta and kiranb, both Eclipse developers in Progress Software's Hyderabad office. Good work guys!
Visit the download page for instructions on how to update your Eclipse installation.
You can always ask questions and maybe find more detailed information on the mailing list.
Run - don't walk - to our bugtracker to report the issue.
Nothing much going on at the moment - this is a small project that needs some work - specifically tests and an update for the latest Eclipse and messaging systems integration. It's low-priority.