SVN mirroring question

[Julian Elischer]

So I need to make a branch of a freebsd branch to do some work related 
changes.
is it feasible to have our own svn repo and mirror a single branch 
into it that we can base
out branch off?  Ialready have a full mirror.. so is it possible to 
keep one branch on
the private repo synced up with the same branch on the mirror?

We actually use P4 so the same question  for P4, except that I already 
have some answers for that....