Don't worry, I'm gonna make sure this won't turn into a language wars. Check forum rules #2 anyway (I guess 1 might apply too)

This is for the FIRST robotics competition.
I was informed of two choices - Java or C (maybe C++?  One of the C's)

All things being equal C++ will be better choice. Of course things rarely are equal

I have no experience in Java - but the team (which I just joined this year) is reusing the bulk of the program from last year, which was written in Java (because one of the seniors last year knew Java).

Well, if they already have something working then it's not a good idea to start total rewrite in different language. It's rarely a good idea in general, but especially when you are competing with someone.

I would love to use Python, but I have no idea how to get a python environment working.

Python is worse then Java in many aspects. It very nice to program, but quite slow. The one thing which is fast in Python and slow in Java is C/C++ interface.

I had to go to a presentation this Saturday just to learn how to get Java/C++ running.

My advice WRT to Java/C++ integration: don't try to push small pieces of task to C/C++. JNI is very slow by design: because it must do lot's of thing WRT GC (objects must be compacted and frozen, etc), so while C/C++ procedure may be faster then Java the switch from C/C++ and back will often eat all adavantages of such hybrid approach.

I don't care much about the detriments of Java, especially because I don't have any viable alternative to present and because I'm not experienced+eloquent enough to communicate the difference well.

You must keep them in mind if you want to write competive Java program. It's very easy to lose track of things in Java - and this leads to tons of unneeded work in runtime. It's possible to write good program in Java, but sadly Java encourages mindless programming so you must resist.

Also, don't forget about the biggest advantage of Java: powerful IDEs. Two top free ones are Eclipse and NetBeans. Two top paid ones are IntelliJ (it has free community version and classrom license) and JBuilder (very powerful but also very expensive). My advice: don't try to program Java without help of IDE (VIM and emacs with bunch of addons can be considered an IDE but only make sense if you were avid VIM/emacs users before trying Java). This is greatest strength of Java and a reason for it's continuing existence.

Also: ask around for what other members of team are using. Often it's easier to use the same IDE as others are using rather then using superior (in your opinion) IDE which does not play well with changes made by others.

And last but not least: learn some version control system if you still have time! My preference will be Git - but only if you are using Eclipse or IntelliJ: NetBeans and JBuilder have unofficial modules (development of official NetBeans plugin started just recently) thus intergration is not as good. But again: talk with other members of a team.

As an "IDE", I use Notepad++ http://notepad-plus-plus.org/ It has hilighting for C,C++,Java, and a ton of other languages as well. It is also small, and can be run from a flash drive.

Notepad++ is fine editor, but it's not an IDE. Good Java IDE includes "code-sense": it detects errors as you type your program, proposes changes to it if you are doing something in suboptimal way, etc. This is what makes it possible to use Java for "monkey programming". The only problem here is the fact that it's not omnipotent and it's suggestions are helpful about 90% of time and the other 10% of time you should say "no" to it's hints. And it only knows simple patterns - it'll never propose to replace hash with rb-tree (or the other way around). Still it's useful tool if you use it as a suppllement to your own brain and not as a replacement for it.