Sounds like you want a scheduler. Check 3rd party sources that will also do e-Mailing. Do a search on the forum for "scheduler" I thought I saw some earlier.
However, once the report is started by the scheduler, then you can use currentdate or any other Crystal date function to accomplish what you need to automatically set any date selection criteria such as lastfullmonth, yeartodate, etc
Again had you been more specific with your information, you wouldn't be frustrated at the roundabout way of solving your problem.
-LW