Because the Eclipse Indigo M6 release it no longer available, installing JBoss Tools 3.3.0.M1 is a bit more difficult that when we first released it.
You will need to install Eclipse "Classic" SDK for your platform from here:
http://download.eclipse.org/eclipse/downloads/drops/S-3.7M6-201103101119/index.php#EclipseSDK
then point Eclipse at the JBoss Tools Development milestone site:
http://download.jboss.org/jbosstools/updates/development/indigo/
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Alternatively, you can use a newer Eclipse or Indigo release:
http://download.eclipse.org/eclipse/downloads/drops/S-3.7RC3-201105261708/index.php#EclipseSDK
or
http://www.eclipse.org/downloads/packages/release/indigo/rc2
then point it at this site to install a preview of the JBoss Tools 3.3.0.M2 release:
http://download.jboss.org/jbosstools/updates/nightly/trunk/
Note that the nightly site is subject to change and will be replaced w/ new bits fairly frequently. If you install fails due to missing artifacts, simply try again.
If you'd rather install a nightly from a snapshot, look here:
http://download.jboss.org/jbosstools/builds/nightly/trunk/
(Choose a build, then enter the "all/" folder to get the update site URL or download the zip.)