I'm occasionally amazed to discover shops that don't use a version control tool. This is almost like finding someone who lives in a modern city but doesn't have an electricity hookup.
I started out with RCS and had a few minor reversions to SCCS. I've used a number of proprietary systems, over the years, but have never found them to be as usable as the open source stuff--first CVS and now SVN.
GIT
Git is a distributed version control system, and the one I'm moving toward. It has tremendous advantages when you're working with intermittent network access.
SVK
Some comments on using SVK for local work from a SVN repository
http://cwilliams.textdriven.com/articles/2007/02/16/svn-and-svk
http://scottstuff.net/blog/articles/2005/07/07/distributed-development-with-svk
http://octopod.info/2006/8/19/managing-multiple-local-mephisto-repos-with-svk
SVN
Switching from CVS to SVN
Guides
http://svn.collab.net/repos/svn/trunk/doc/user/cvs-crossover-guide.html
http://www.onlamp.com/pub/a/onlamp/2004/08/19/subversiontips.html
Instructions