Measure RDP Traffic - 2003 Server

Hi all,

I have a few windows 2003 terminal servers that a number of clients utilize.
I'm being asked to provide traffic reports (so they can be charged for data)
but am not sure where to start!!

All the servers including the domain controller where their data is stored
are windows 2003 R@ sp2 servers. There are approximately 600 users that are
all in different ou's in active directory. So for example company1 may have
15 users in their ou and comapny2 may have 80 users. I need to collate the
usage for each OU as apposed to each user.

I need to measure all thier RDP traffic so printing etc...

Any ideas?