Sorry, had to leave for a bit
When in Virtualdub, under File click Capture AVI. Then under Video click Source. For RCA inputs you'll want to set the Select Video Source to Video Composite. Then when you're ready to capture, click the Capture tab and select Capture Video. On the right-hand side you'll be able to see the recording progress. Click the mouse anywhere on VirtualDub to stop capturing. When you are finished, click File and select Exit Capture Mode.
Depending on what codecs you have installed you may want to go into the Video tab after you enter capture mode but before you start capturing and select Compression to change what video format you capture in.
The resulting AVI can then be manipulated in any program that handles AVIs.