This burned several hours of my time so I thought I’d add this post to the others that I found on the Intertron.
I had debugged every possible angle when trying to get a Vista machine to checkout a repo from an svn+ssh server. At last I figured it had to be a subversion client-server version problem, rather than an issue with the SSH keys, and so it was.
For reference, I’m using TortoiseSVN 1.5.5 and the server is running openSUSE 11.0’s subversion-1.5.0-96.1 package.
The solution, as many have stated, is to downgrade to TortoiseSVN 1.4.8.