What is the best way to export iphoto library to a certain folder structure?
Yes. Couple of possibilities


If you have the latest version of iPhoto 11 there's a limited option in the Export dialogue. (File -> Export. Note the 'Subfolder Format' option in the Export dialogue. Remember you actually have to have an Event selected for the option to appear)
For earlier versions, or more granularity, Apps like iPhoto2Disk or PhoShare will help you export to a Folder tree matching your Events.