Recently I have find out that TortoiseSVN (surprise, surprise) supports git. So you can just checkout git repository using TortoiseSVN, and even to reference external git reposi
TortoiseSVN does not support Git.
I guess that you tried GitHub repositories with TortoiseSVN. Yes, it works in general and should also work with any other SVN client. GitHub allows SVN clients perform simple operations with its repositories through a special transparent proxy (I may be wrong, but that's what I read). So it is not TortoiseSVN that uses a special mapping schema, it's GitHub that reports Git revisions to SVN client in a form that the client can digest. :)
There is another Tortoise* client -- TortoiseGit. It takes Windows Shell integration idea and tries to map it to Git commands.