Subversion AND gem rails howto?

I have been using rails on Debian Sarge since May of last year. I
initially
gem installed rails as root and since then I have been gem updating the
installation. I have had no trouble with the installation or
development.
Now feel that I’d like to use svn to get edgerails to be able to use
nifty
features such as RJS. Some of the threads on the subject talk about
svn:externals in the vendor directory. This means I’d have to do this
for
each project?
Can some one please tell me how to manage a svn edgerails version on my
machine which can be shared between all projects? I am the only user on
the
machine and so installing it in /home/me won’t be a problem.
The question is how will the edgerails co-exist with the gem installed
global rails? If I say rails some_new_app who will create the project
…or
more importantly how can I choose which installation to use for a
particular
project? Can I do something like… /usr/bin/rails for the gem installed
one
vs. /home/bin/rails for edge rails? How can I setup the environment so
that
rails pulls in all the correct libs and dependencies which currently are
managed by the gem package (I think).

Thank you,

bakki kudva