Thin Client license metering

Our current environment is desktops and laptops running Windows NT 4.0 with NetWare 5.1 as the NOS. We have 18 sites througout the world. Licenses on the workstations are handled by local IT resources.
We are moving to a thin client environment using W2003 Servers spotted in two global data centers and using Active Directory. All thin client appliances and a small number of laptops will point to the central servers for applications and data storage. We are also rationalizing our applications from 1500+ to 100.
At issue is how to manage and meter application licenses. Anyone have guidance or a neat commercial package which handles this? Does putting licenses in a central area make sense?