Working through an issue on Eclipse 3.2. Everytime I open, edit, and save a build.xml file, Eclipse freezes up for 5 - 10 seconds. Not a huge deal, but it's relatively annoying if you're not in a patient mood (and I hardly ever am). After Google search, I found that this is a known issue for Eclipse 3.2.
And the workaround is relatively simple.
Uncheck "Provide proposals for user defined tasks" under Windows > Preferences > Ant > Editor > Content Assist.