Grammar Girl says this:
Here's the deal: you can use the word “between” when you are talking about distinct, individual items even if there are more than two of them. For example, you could say, "She chose between Harvard, Brown, and Yale" because the colleges are individual items."
Speaking of Grammar Girl, DailyLit.com is offering The Grammar Devotional by Grammar Girl for free, one tip at a time. Click on the link and you can sign up for it.
Back to the question. It's okay to use between for three or more whatevers according to the OED, M-W's Dictionary of English Usage, and most of the big guns of English usage. The M-WDEU calls the notion of between only for two and among for three or more unfounded. I agree and usually use between for many individual and separately identified items (groups, especially) in biomedical articles. No journal editor has complained in 15+ years.