What can you do with Vegas that you cant do with open source software?
Hmmm seems you are not alone, can't import video into Vegas seems a very common problem. Check out Google
http://tinyurl.com/3ydwnvh
If you feel you must, for whatever reason, try a codec pack then I strongly advise you to Image your system before installing it. Then if the brown stuff hits the fan it will be a simple matter to get back to square one.
Oh did I mention, never install codecs over themselves, they don't like it. Always uninstall existing before installing new or updated versions. In case you have got xvid into a mess, you can obtain a clean version by uninstalling it then search C:\WINDOWS\system32 (or win 7 equivalent) for xvid to catch any remnants. Delete any found. Now you can install a clean xvid.
Your problem might be more to do with your source video rather than codecs. Just a thought.
---------- Post added at 11:58 ---------- Previous post was at 11:25 ----------
Just noticed this.......
From
http://www.videoforums.co.uk/sony-ve...y-vegas-2.html
"Has anybody tried
ENABLING 3rd Party CODECS in Preferences in Vegas?
By default this remains OFF. I've never had to play with this setting."
Might be worth a look?

---------- Post added at 12:12 ---------- Previous post was at 11:58 ----------
And also..........
From
http://www.videohelp.com/forum/archi...s-t289247.html
"Actually, the solution to this problem was to merely change the fourcc code of the avi files to "DIVX" (all caps) using
avic.exe (small freeware program). Sony
Vegas and
DVD-Architect won't recognize any avi files undless fourcc is "DIVX", even if it's a xvid, doesn't matter."
I'm beginning to think Vegas might be a load of overpriced carp.