SVNProtocolHandler for Internet Explorer allows browsing svn:// urls from within the Internet Explorer. No need to install a Subversion client, just use IE. This also adds the benefit that you can click on svn:// links and quickly access the URL you received from a colleague via email.
Subversion repositories served with Apache have the nice built-in feature: the repositories can be browsed with any webbrowser at no additional cost.
For Subversion repositories served via svnserve, this is not possible because browsers don't understand that protocol.