Each time I set this up I always have to google to remember how to do it. The last time I set it up I came across James Kovacs' post on the subject which works great. The only thing I usually end up adding is the --listen-port=x since many clients do not allow me to open up a new hole in the firewall so we end up using port 443 which works great.
I actually couldn't find James's post (I think I was googling subversion windows service instead of svn windows service) and found it through Corey Ippolito who references James in his post.
So hopefully I never have to look hard for this again. :)
Cross-posted from blogs.sqlxml.org