I suppose this command would help:
cvs diff -N -c -r RELEASE_1_0 -r RELEASE_1_1 > diffs
where RELEASE_1_0 and RELEASE_1_1 are the names of your tags.
You can find a little more information on cvs diff command here
plus it should be fairly simple to create a script to make report more suitbable for your needs, ex: number of files changed, created deleted etc. As far as I know the most common cvs GUI tools (wincvs and tortoise) do not provide something like this out of the box.
Hope it helps ;)