Rybka 3-1 CPU.exe versions = Rybka Single Processors known as plain Rybka 3.
Rybka 3 w32.exe versions = Rybka MP also called Deep Rybka w32 bit.
Rybka 3.exe = Rybka MP x64 also called Deep Rybka 3 x64 bit.
So if you have a 64bit system, you want to select the "Rybka 3.exe" which also comes with Rybka 3 Dynamic.exe, Rybka 3 Human.exe, and Rybka 3 960.exe - (these are the MP or Deep Rybka 3 versions).
If you have a 32bit system, you want to select the Rybka versions with "w32" (these are the MP or Deep Rybka 32bit versions) which also comes in Rybka 3 w32.exe, Rybka 3 Dynamic w32.exe, Rybka 3 Human w32.exe, and/or Rybka 3 960 w32.exe.