Okay, some of you may have known this, some may not, but I figured it could be useful for some people.
Those of you on standard Ubuntu Linux, which I figure most people should, may have figured out there is technically no level editor out for it yet. Most of you have probably also heard of gonstruct, the...replacement of sorts for it. If you haven't, take a look at this:
http://londeroth.org/~fry/gonstruct/
Now, there's a whole set of annoying things to get it running on Linux.
Forget all that.
Go download wine. It allows certain Windows applications to run on Linux (Zeke you are a GOD for showing me this). Download the windows executable file for gonstruct. Then, if you don't want to search around for it, drag the .exe onto your desktop. Right click it, under properties check, "Allow execution as a program" or whatever the right phrase is under the rights tab. Then run it using wine. It should setup just like a windows program, and it'll work fine. Much easier.
By the way, after you're done, look under applications, there should be a wine tab. Go into that, programs, gonstruct, and gonstruct again should start it up. Have fun!