Strider,

My tool / solutions for generating radius reports is here:

http://mike.wnol.net/project/radius

The solution uses MySQL and PERL.
Once you build the database, you can run SQL queries to find the information you seek. The page gives simple step-by-step instructions which have been followed by many a person interested in radius log parsing.
If you have any questions, drop me an email.

Go in Peace!
-UUOC