Sorry to bear the bearer of bad tidings Lance but, as of right now, it can’t be done 🙁
There was a thread about this issue on another Vegas forum recently and this was Sony’s response:
“IF there were a 3rd party capture/print module to get files on and off of the computer and IF the codec were something Vegas could access, you’d be able to do DVCPRO HD in Vegas 4, 5, or 6.
DVCPRO50 currently “works” similarly- all you need is the codec installed to edit the files, i/o is handled by something external.”