Associating existing Eclipse project with existing SVN repository
Solution 1:
Team->Share project
is exactly what you need to do. Select SVN from the list, then click "Next". Subclipse will notice the presence of .svn directories that will ask you to confirm that the information is correct, and associate the project with subclipse.
Solution 2:
I just wanted to add that if you don't see Team -> Share project, it's likely you have to remove the project from the workspace before importing it back in. This is what happened to me, and I had to remove and readd it to the workspace for it to fix itself. (This happened when moving from dramatically different Eclipse versions + plugins using the same workspace.)
subclipse not showing "share project" option on project context menu in eclipse