Hi There,
I am guessing you are looking for something that will give you total data per user over a selected time period. To do this you will need two sources of data. Firstly you could get the data quantities from something like SolarWinds NTA or if you don't have flow options you could look at setting up a SPAN port at the network core and get something which can do traffic analysis on network packets. Technologies like this will give you outputs like top IP addresses based on data\bandwidth
Next up you will need the usernames. You can either check your domain controllers or look at something which can 'sniff' usernames from network packets. SolarWinds don't do any correlation of usernames to traffic flows\sessions yet so you will need to do this manually or look at getting a 3rd party tool which integrates with Orion
The company that I work for has developed an application which can integrate with SolarWinds products and provide user reporting. Check out the demo at the link below, the graphic top left shows top users and you can also drill-down. It only lists 5 users in this demo but each user on the network is tracked.
http://demo2.netfort.com/Orion/SummaryView.aspx?netobject=&viewid=1
Darragh