No, you can't contribute to your Roth IRA more income than you earn ("unearned" income like interest, investments, etc doesn't count.) The only exception is if you are married and have a working spouse, your spouse can contribute for both of you.
On another note, one good thing about this current economic situation is that it has made Roth Rollovers even more attractive this year. As you might already know, it is possible to spread the tax burden out over a few years if the rollover is done this year. With market values so depressed, the tax burden is minimized even further. It's a good time to be a Medical Student with 401ks and IRAs that can be rolled over 🙂
EDIT: Actually, it is for rollovers in 2010 that allow you to do tax averaging over 2 years, so the timing isn't quite perfect (hopefully we will be out of this market slump by 2010.....)