Exchange 5.5 priv.edb

My exchange PRIV.EDB has grown to 66G! Its filled my drive. I only have about a dozen email boxes on it and only as pop3. How can I see whats filling it up and clear it out? I have a second drive with 44G on it and I tried to do a defrag (compress) and it stopped when the second drive was full at 44G so I dont think it was getting any smaller. Since everyone is pop3 I dont need to store any more then what hasnt been downloaded yet (and even then only for 15 days).