Here is a freeware tool FavBackup, which will help you backup and restore not only bookmarks but all other settings of your browser also like preferences, cookies, history, saved passwords, extensions, etc.
This tool supports Firefox (2 -3.5), Internet Explorer (6 – 8), Google Chrome (1 – 3), Apple Safari (3 - 4) and Opera (9).
FavBackup is a simple and easy to use program which requires no installation. Just run the program, select your browser and select Backup and or Restore.
Click next and choose the items (bookmarks, cookies, history, preferences, etc) that you want to backup and or restore.
Now select a location (example USB drives) to backup your selection or to restore from. FavBackup works on Windows 7/Vista/XP/2000 systems. Download FavBackup