convert your avi clips to be encoded to Lagarith (you can do this in Virtualdub Mod very easy)
if the file is too big then
1. disable the audio and
2. use these buttons to select parts you want to use:
Vegas really likey the lagarith codec...
plus its best to keep all your source footage the same kind of file anyways...
ps. ive installed 7, but i havent used it yet O.o I can still use Lagarith files in my program... (and editing with VOBs is interesting @_@)
I also refuse to install FFDShow onto my system... personal preference... and ive no clue what CCCP is, but Vegas SHOULD have no problem with Lagrith.