I generally go to Google to search, you can enter this into Google:
Sandy Berger site:www.freerepublic.com
Also filter out to posts within the last 24 hours. That has a pretty good success rate.
2. Sandy Berger, Former National Cecurity Adviser, Dies (Clinton Crony, aka Sandy Burglar) [Locked - no new replies]
3. Sandy Berger, former national security adviser, dies
Start with the broadest search possible. In this case, because of the uncommon spelling of his last name, simple search title for "Berger." If you get too many results, tighten the search with more words.
As dfwgator says, you can use Google Advanced Search to search FR and narrow things down to a specific date range, too. I find that very helpful.