and here from :
http://www.macosxhints.com/article.php?story=20060627105559861
"One thing that bugs me is that there is no option in Safari to alphabetize bookmarks. I had a crazy idea about how to accomplish this, and it seems to work. Hopefully I'm not missing something more obvious. "
"What I did was open the Bookmarks window (Bookmarks: Show All Bookmarks), put the links I wanted to alphabetize into a folder, and then dragged that folder into the Finder. The Finder alphabetizes the bookmarks; you can then just drag the folder back into the Bookmarks window. You probably have to set the Finder to arrange files by name before it will work. Hope this helps! "
"robg adds: When you drag the folder back, you'll now have two folders, the original and the sorted one. Just delete the original, and you're set. You can also do this without first creating a Safari folder. Just select all the bookmarks to be alphabetized, drag them into a new folder in the Finder, open that folder (make sure it's set to sort by name or use column view), then drag the now-sorted bookmarks back into Safari's Bookmarks window. Again, you'll have duplicates, so just delete the originals (which will be grouped above the newly-placed list). I wonder if any of this is scriptable..."
Hope that helps....