Adding a Counter based on Criteria

Hi folks, new visitor/poster here. I was wondering if someone might have an opinion on how to accomplish a task I wanted to complete in Excel.

I manage a Customer Support desk, and I have a report from our Chat client exported in Excel. The report shows start and finish times for each chat an agent took during the course of the day. What I was hoping to do was to take the start and finish times for each chat, and discovering how many concurrent chats each of my agents had. What I have, for example, is this.

Chat Start Time Chat End Time Operator Name
2/14/2012 7:06 2/14/2012 7:15 Agent A
2/14/2012 7:33 2/14/2012 7:43 Agent B
2/14/2012 7:45 2/14/2012 7:48 Agent A
2/14/2012 8:52 2/14/2012 8:56 Agent C
2/14/2012 8:01 2/14/2012 9:56 Agent B
2/14/2012 9:39 2/14/2012 9:58 Agent C
2/14/2012 8:47 2/14/2012 10:02 Agent B
2/14/2012 10:08 2/14/2012 10:22 Agent A
2/14/2012 12:02 2/14/2012 12:21 Agent B
2/14/2012 12:27 2/14/2012 12:36 Agent A

Is there some function I could use which would advance a counter somewhere if the duration of an agents first chat encompassed the start time of following chats?

This has melted my brain, and it might be asking too much of Excel, but maybe some boffin out there has done something similar in the past?

Thanks,
ES.

I was afraid that was going to be an answer. I could stumble my way through it. Been a while since I have used VB.