ouch! I'd try this on a copy of your cvsroot first, but you may be able to get away with doing another import of the last non-broken vendor sources, and then in your working copy doing a 3-way merge between the last good version and the new good version into your current -HEAD (which should be a null diff, but bring cvs's idea of -HEAD back to the right spot)... This would leave a record of the botched import in your repository, but should get your current development sources back on track....
NB: I haven't actually tried this myself, so it's all theoretical at this point...
