If you got space on the hard drive (check Activity Monitor) create another user (B) and log into that and see if the problem continues.
You might have a corrupt .plist file in the original problem user (A)
Log into the problem user (A) your Safari history.plist file is in your Users/NAME/Library/Safari/History.plist
You can just remove this someplace else and it should be rebuilt the next time Safari launches.
Also download the free OnyX for Leopardhttp://www.titanium.free.fr/pgs/english/apps.html
Log into a Admin user
Under the Verify>Preferences is a plist (preference file) checker, run that. Show only corrupt files.
Screen copy the problem list for reference and then locate the problem .plist files and move them someplace else, they will be rebuilt upon next launching of the browser or program.
Also you might want to run all the maintenance and cleaning while your there in Onyx, you can cancel the needed reboots to do the other cleanings, just make sure you do reboot after quitting Onyx. It takes bit and sort of resets your machine back to the original install state on the system level, cleans caches, spotlight etc. Won't hurt your machine or files any, do run the checkers first. Your spotlight/mdworker will eat your cpu's for a bit until it's done, Onyx cleaning and maintenance will make your machine a bit more snappy.
See if any of that works.