The simplest method is to use the TOP keyword.  So, suppose you want the most recent hundred entries.  Have your SQL look like:

SELECT TOP 100 *
FROM MyTable
ORDER BY MyDate DESC

This can also be done in Crystal, using the Group Sort Expert.  Unfortunately, it's a bit less straightforward, as you can't simply do a Top N on all the records.  Instead, create a Group based on the unique ID of your records (hence, generating one "group" for each record).  In the Group Footer, put a summary field for the Maximum of the date field in question.  Then, use the Group Sort Expert to do your Top N.