There may be easier ways, but the following steps are the ones I take to roll back a specific revision.
Find the revision that you wish to back out. This can be done with various tools, but 'svn log --limit 10' will probably do the trick. Once you have the offending revision you are ready to get started. (Revision X in the example is the revision that needs to be rolled back and revision Y is the revision that came immediately before X [i.e. X-1])
- svn diff -rX:Y > a.patch
- patch -p0 < a.patch
- svn commit
Again, there is probably an easier way to do this (which is part of my motivation for writing this entry), and obviously this solution depends on having 'patch' available.