Re-attaching source files to existing SVN

You first need to create a working directory and the only way to do that is to do a checkout and get the files from the server.

HOWEVER, when you said source files, you meant working directory, you may be in luck anyway. Does your source files contain that .svn directory? If so, you have a working directory, and restoring your working directory on your new machine should work just fine. Just make sure you're working with the same version of TortoiseSVN that you had on the old system: Especially if one is pre-1.7 and the other was post-1.7. That's because the working copy layout changed from version 1.6.x to version 1.7.x. See if you have the .svn directory in each directory of your Subversion working directory, or only in the root. If it's only in the root, use TortoiseSVN version 1.7 or greater. If it's in all the directories, use TortoiseSVN version 1.6.x.

If you don't have those .svn directories (and they might be hidden), then you don't have a working directory. You'll have to do a checkout, and then manually move the files over that are different. Take a look at Beyond Compare to help you with this task.

Because your sources are in Working Copy (Copies) of repository (your have .svn subdir(s)), which continue to exist, just install TSVN and you can contibue too work with repos (version compatibility warning still apply, but yuo'll get notify and instructions in bad case)

You can don't worry about local changes - on Update you WC local changes will be merged (auto or by hand) with incoming changes