Hi man, I see your post is dated 2011, but just in case you still have the problem with capturing with your Canon XHA1 to your PC, this is what work for me:
Download and install Adobe premiere 7 (trial) and try it (it should work fine), once you had successfully capture your video then close Adobe Premiere and open Vegas, it should work this time.
Alexander
P.D. Sorry about my English, I’m from Venezuela and I just wanted to share this after spending more than a year trying to get a solution for this!