there are 2 main methods to backup a svn server, first is hotcopy that will create a copy of your repository files, the main problem with this approach is that it saves data about the underlying file system, so you may have some difficulties trying to repostore this kind of backup in another svn server kind or another machine. there is another type of backup called dump, this backup wont save any information of the underlying file system and its potable to any kind of SVN server based in tigiris.org subversion.
about the backup tool you can use the svnadmin tool(it is able to do hotcopy and dump) from the command prompt, this console resides in the same directory where your svn server lives or you can google for svn backup tools.
my recommendation is that you do both kinds of backups and get them out of the office to your email acount, amazon s3 service, ftp, or azure services, that way you will have a securityy backup without having to host the svn server somewhere out of your office.