I also tried to find some kind of integration between a CM tool (like ClearQuest) and CVS as a versioning tool.
I would like some kind of interactive prompt at commit time urging the developer to chose one of the requests assigned to him, as a justification for this commit.
This would allow a better status accounting and automated change set gathering.
You'd do better to check out cvshome.org to get a grip on how to make CVS act upon user operations like commit. Answers are not likely to fit the format of this forum; it can probably be done but you would have to tamper with the sources. :-)
This section on triggers and logging is probably a good place to start - if you are registered at the site.
On the other end, ClearQuest would be well suited to do the reverse operation; when opening a Change Request (bug, Defect, Trouble Report, Enhancement Request...) you could execute a CVS checkout on applicable modules.
And have the workspace linked to the records in CQ.