First of all, I'm not really familiar with RadRails. The FAQ says they use Eclipse Subversive for Subversion support. They link to the Subversive manual for advanced topics from that FAQ page.
The way to import it manually (with the commandline client) is probably to first create the repository structure you want, by using (for instance):
svn mkdir http://server/svn/repos/trunk
Then checkout the empty directory in your project root, so you get a working copy where you can add things:
svn checkout http://server/svn/repos/trunk c:\MyProject
Then you can add files and directories