There has been some Problems with Eclipse on Ubuntu 9.10, f. e. clicking on buttons are sometimes not working.
This is due to a changed behaviour of the underlying graphics and widget library GTK+. See the following links:
Eclipse Bug Tracker: [https://bugs.eclipse.org/bugs/show_bug.cgi?id=287307]
This bug should be fixed in Eclipse 3.5.2.
To launch 0.5.1 in Ubuntu 9.10 try using: rpgng -vmargs -Dorg.eclipse.swt.browser.XULRunnerPath=/usr/lib/xulrunner