TortoiseSVN is a great Windows Shell Extension for Subversion.
All of my Google searches suggest firewall issues, but the network hasn't changed overnight since it last worked. Might help if this article had a section dealing with a few simple Subversion issues.
$ svn co http://svn.automattic.com/wordpress/trunk/
svn: REPORT request failed on '/wordpress/!svn/vcc/default'
svn: REPORT of '/wordpress/!svn/vcc/default': 400 Bad Request (http://svn.automattic.com)
Yearginsm 02:26, 25 Mar 2006 (GMT)