I can't remember how to edit the 'Open with
' menu, but it can be done. However, it wouldn't be such a mess normally your prebindings are messed up. The easiest way to try and fix this is, assuming you haven't already, update to the latest version of OS X. If you're already up to date, you can either re-apply the 10.4.10 combo update (I think you're running Tiger, from that screenshot) or search the forums or use Cocktail to rebuild them manually.