Perhaps the most important way to familiarize CVS users with Subversion is to let them continue to work on their projects using the new system. And while that can be somewhat accomplished using a flat import into a Subversion repository of an exported CVS repository, the more thorough solution involves transferring not just the latest snapshot of their data, but all the history behind it as well, from one system to another. This is an extremely difficult problem to solve that involves deducing changesets in the absence of atomicity, and translating between the systems' completely orthogonal branching policies, among other complications. Still, there are a handful of tools claiming to at least partially support the ability to convert existing CVS repositories into Subversion ones.
One such tool is cvs2svn (http://cvs2svn.tigris.org/), a Python script originally created by members of Subversion's own development community. Others include Lev Serebryakov's RefineCVS (http://lev.serebryakov.spb.ru/refinecvs/). These tools have various levels of completeness, and may make entirely different decisions about how to handle your CVS repository history. Whichever tool you decide to use, be sure to perform as much verification as you can stand on the conversion results—after all, you've worked hard to build that history!
For an updated collection of links to known converter tools, visit the Links page of the Subversion website (http://subversion.tigris.org/project_links.html).