Darn!
Never keep your original app on your desktop . . .
Always in your applications folder.
But I guess you already learned that, eh?
To put an alias in your dock, drag the Safari icon from your applications folder to the dock. Your actuall application will remain in the Apps folder.
To get Safari back:
You could try doing a 10.4.6 COMBO update,
or even better, 10.4.8 COMBO update.
Or you could use Pacifist to just install Safari
http://www.versiontracker.com/dyn/moreinfo/macosx/12743
Keeping fingers crossed for you!