To merge a branch into a HEAD, simply go to the local sandbox for the mainline code, and run:
%cvs upd -jBUGGY_BRANCH
A HEAD can be merged into a branch too using the same method.
To search for the conflict, from the command line, run:
%grep -r “>>>>>” *
The result should be a list of files which have the “>>>>>” content. Most likely, indicating the CVS conflict.