OS X Snow Leopard 10.6 requires a Mac with an Intel processor and a few other details; here are the OS X 10.6 technical specifications (including system requirements). The About This Mac can get you system details, if you don't already know them.
I don't know off-hand of an Intel processor at 667 MHz; that was one of the speeds encountered with the G4-class PPC systems, Those don't support Snow Leopard AFAIK. (The most recent similar G4-class PPC Mac was released around 2003.)
Is the Safari icon you are referring to as missing the Safari icon that's often in the dock?
If so, does Safari exist in the Applications directory?
If it does, drag Safari back to the dock.
If Apple Mail.app is no longer set up, then does reconfiguring it work?
It's also possible that there are issues or problems with the upgrade; that's happened occasionally over the years.