I don't know what you're using for an editor - I use the RCP rather than the full Eclipse plugin set. Either way you can get it from the BIRT download site (download.eclipse.org/birt/downloads/). Go to the Archived Builds page to find the 2_3_0 link.
Whoops, I may have misread - did you want 2.3.0 or 2.5.0? Either way you can find both through the archived builds.