Hey!
I've been trying out polyphasic sleep for a while, but am not totally polyphasic yet (I haven't really put my heart into it). You might still want to learn from my mistakes 
The one thing I highly recommend, is to find original ways to wake yourself up, and to KEEP YOU AWAY FROM THE BED 
(hint: one alarm clock isn't enough)
I've often found myself falling right back to sleep when waking from a nap... specially around the 4AM time frame.
Another advice is to get used to napping frequently prior to trying the switch... If you can find two 30 minutes spots in the day to fade away, it'll get you used to napping. Then three. then maybe four?
By the way, a nap should NEVER exceed 1 hour. And a 'core sleep' cycle should never be LESS than 4 hours...
All in all, my experience with semi-polyphasic sleep has reduced my average sleep time (to a not-tired state) from over 10 hours to around 6. i.e. I can work longer with less fatigue when I nap 
I might experiment further later this month, when I get to finish my last final 
HTH!
Cheers!
PS: You might want to find that book called "Why we Nap" at your local library
it's quite informative!