I don’t use Vegas but you should probably check 2 things:
1. Your capture settings in Vegas match the material you’re trying to capture (dv? hdv? I assume hdv)
2. On the XHA1, unplug firewire cable. In signal settings, make sure playback is set to auto, and also make sure down convert is not set to on if you’re trying to capture HDV. (make sure firewire is not connected or some settings will be grey’d out.
switch off A1 andconnect firewire cable, switch on the A1
good luck!