So you finally have your own svn repository. But you need to use external code as well. And you want to keep track of changes in those external code. Then use svn:externals. This tells subversion there are external subversion repositories destined to blend into the current folder. I learned this from a script thanks to Wim Leers
First let's create an externals to a repository in the current directory.
If this fails configure an editor like this
svn propedit svn:externals .