I messed around with trying to get NTLM authentication working via SASL using svnserve, but it doesn’t appear anyone has figured that out or maybe it was broken at some point.
I was trying to avoid using HTTP for SVN to avoid traffic overhead, but it appears I had no choice. I installed all the separate pieces (Apache, Subversion, and mod_auth_sspi) instead of downloading one of the many prepackaged setups (VisualSVN, überSVN, etc.).
It went pretty smoothly referencing a web page I found. I hit a snag where it worked in the browser, but not with TortoiseSVN or the Subversion command-line client. Once I enabled Basic authentication, that problem was solved.
Next up, installing ViewVC!