Checking out and building Teiid Designer with Eclipse is probably much easier than you think.
Get Eclipse SDK
If you do not already have it download Eclipse SDK 3.4.1 or later visit: www.eclipse.org/downloads.
SDK is important since otherwise you do not have the PDE plugins which is needed for plugin development.
The easiest is to get Eclipse JEE which is a full SDK bundle with the required plugins.
Get the source
You can checkout the complete trunk/branch/tag of Teiid Designer via command line or your favorite svn client.
Using Eclipse to do it is can be a snap.
To get committer trunk:
To get anonymous trunk (readonly mirror):