Measuring concurrent users on NT w/Lotus

We are running Lotus LearningSpace 5.0 on a Dell 6400 with NT4 O/S. We need to find out how many concurrent users are hitting the box. Our shop uses WebTrends to do this in most of our standard IIS environments but we don’t know if WebTrends is compatible with Lotus LearningSpace.

Lotus cannot give us a recommendation. I was wondering if any of you have experience with this and, if so, what do/did you use to measure concurrent useage?