Rybka and Fritz 12 are engines. You may think of them as engines of a car. GUI's, however, are different, they are interfaces (cars) that run engines.
If you purchase Rybka or Fritz from chessbase, they will have the same GUI, but the different engine. So there will be no difference in their handling of databases.
So, you don't have to purchase two databases.
There's one thing I don't understand though, why purchase them both? Rybka is much stronger than fritz, and they have the same GUI as I mentioned.
As to your other question, yes, you do need a multiprocessor computer to run Deep Rybka, and you have one (hence the Dual-Core) !
Just make sure you don't get Rybka Aquarium (the convekta GUI for the same Rybka engine) instead, it seems you don't have much experience with this and aquarium demands too much of that.
I'm ready to purchase Rybka 3 and Fritz 12 for post mortem analysis and playing against a computer. Also, I'd like some database to keep everything organized and be able to run searches. I don't have anything but chesspad to save pgn files, and my folder system is getting to be quite a mess!
www.chessok.com sells different Rybka/Aquarium bundles,i.e., Rybka/Aquarium and Aquarium 2010. It's confusing. www.chessbase.com sells Rybka 3, Fritz 12, ChessBase 10 and ChessBase Light.
Question: Would one database work with both Fritz and Rybka, or would I need to purchase two databases?
Last: There's Deep Rybka 3 and Rybka 3. Do I have a multiprocessor to run Deep Rybka? I have a Dell Inspiron Laptop 1545. This is what my computer says:
Processor: Pentium Dual-Core CPU T4200 @ 2.00 Ghz, RAM 3.00 GB
System: 32-bit Operating System, Windows Vista
Thanks for the geek sqaud input in advance!