I don't know Vegas, but generally it works like this:

- Download and install POD HD ASIO Driver

- Start general POD HD ASIO configuration in windows: Start-> All Programs -> Line6 -> Tools -> "Line6 Audio-Midi Devices"

- Configure ASIO buffer size (to get sure start with 512k and medium block size, later you can reduce as long as there is no crackling)

- Level your recording inside POD HD ASIO driver (use recording volume slider and take care of +18db = off at first)

- Choose POD HD ASIO Driver inside Vegas Software Configuration

- Maybe you also have to level your own sound preset by e.g. using the Volume knob

- A little trick to avoid unnecessary listening delays while recording (latency): Keep the monitoring slider open inside the asio driver, but deactivate the monitoring function of the recording software.