I\'m really confused. I want to do something that a) seems like it should be pretty simple, and b) other people must do all the time, but I cant find out the best w
The vendor branches link you provided does effectively describe the process of what you want to do. It is a perfect solution relative to allowing you to do a straight update (import) of the vendor branch, and then as you allude to, will then allow you to merge the vendor's updates in with your changes in the main development branch.
The problem is that Subversion really doesn't provide direct support for file renames and moves of files between directories for the successive update from the vendor code because you are just getting snapshots of the source files' content....something needs to run the commands into the version system to indicate what changes are being made to the tree of file names that make up the new version. This is the purpose of the svn_load_dirs.pl script process. It helps you to get your version history manipulated around to match up the branches so that you can then proceed with the merge. If the vendor didn't rename and/or move files around between versions you imported, you would not have this problem.
In any case, the process described there is what you/need to do.