Anyone know what these files do?

Had vegas movie studio 6.0b running on my machine for a while (windows 7) and working fine. I goto use the capture app to capture video via passthrough, it crashes. Every time I startup now I get the splash screen and nothing happens.

So I installed 9.0b trial and same thing. I found instructions to fix the problem. I ended up renaming the AVCDevices.dll and extviddev.dll to *.old.

This fixed the startup problems. I still cannot capture passthrough. The passthrough app just hangs. Any ideas?