I attempted to adapt to polyphasic sleep last year.........
It was the worst 2 weeks of my life, and i ended up failing because I decided to quit out of concern for my health.

If anyone tries to do this, I have a word of advice for you: Make SURE you don't oversleep often. That will lead to absolute failure.
You will sleep through your alarm clock if you aren't careful.
This group was a big help in gathering information though:
http://groups.google.com/group/Polyphasic?hl=en&lnk=When your body adapts a little, you will definitely know. I had a night's worth of dreams in 20 min once. (It felt amazing)

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It is interesting, but I don't really recommend it.
Good luck though