Threading Help

I am working on a GUI based application that will kick off three threads. The first thread has a System.Timer event that creates a List object. The timer resets itself after it runs out, so the thread will run for n amount of time. The second thread has a System.Socket that also creates a List object when data is received. This thread will also be running for n amount of time, as it loops to wait for more connections. The third thread needs to get to the information contained in the List objects in the first and second threads to correlate the data in each list. I have been looking into it all day, and I cannot come up with a good idea of HOW to access the data in those lists while the threads are running. I don't have much in the way of code yet to post, as I am still in the planning stages at the moment, so I am looking more for a technique answer than someone solving my code problem for me.

As always, thank you for the help!