Thank you very much it was very helpful, but hadn't Rybka won a lot of computer championships?
Best Engine?

rybka 4 was never the best, even critter and the first version of houdini (both free) are ranked higher
http://www.computerchess.org.uk/ccrl/4040/rating_list_all.html
According to that list Houdini 1.5 is rated better than Critter and Stockfish.
I've let them have quite a number of goes at each other and Houdini was left quite far behind:
1. Critter_1.6a_64bit 13/20
2. Stockfish_13051320_x64_modern_sse42 11.5/20
3. Houdini_15a_x64 5.5/20
Also note that there's almost daily updates for Stockfish if you use the Dev version. The one I last tries was from may 13th. I now downloaded the newest one and will see if it now can get to the top of the free-engine-rating.

Does anyone know where can I download Houdini 3 pro 64 bits? Thank you very much if anyone can help.

Hi, does anyone know how to import Houdini 3 64 to Chessmaster 11? I tried but it says the file can't be read.
Also, do the program affect the engine? For example I use arena 3, is there a program that allows the engine to work at its best potential or there is no such thing?
Also I believe the opening book of Houdini is not perfect, I think Herman has a better book, am I wrong about that?
Thank you very much if anyone can answer those questions.

Chessmaster 11 can only directly import Winboard engines. Since Houdini is a UCI engine, it can't be directly imported into Chessmaster. Houdini can be indirectly imported if you use a Polyglot adapter between the GUI and the engine, but you'd have to learn how to do that.
I don't think your choice of GUI would have much of an effect on the performance of the Houdini engine.
Edit - I almost forgot. I can't remember if Chessmaster can even run a 64-bit engine. You might be forced to use the 32-bit version of Houdini with Chessmaster. If you decide to try the Houdini/Polyglot combo in Chessmaster, I'd get the 32-bit version working first, then try the 64-bit version, which might not even work.

I believe Houdini Pro 64 interfaces only with Chessbase/Fritz.
I'd be shocked if that were really the case. The manual says nothing of this restriction. And it doesn't make any sense from a marketing perspective to lock out everyone not using a Chessbase/Fritz GUI.

Houdini can be indirectly imported if you use a Polyglot adapter between the GUI and the engine, but you'd have to learn how to do that.
And how can I learn to do that? It's interesting.

There's information on how to set up polyglot adapters (also called UCI2WB adapters), but it's a little disorganized. You can probably get a lot of the information just by Googling terms like chessmaster, polyglot, uci2wb, winboard, uci, adapter.
A few useful links are:
http://wbec-ridderkerk.nl/html/details1/PolyGlot.html
http://horizonchess.com/FAQ/Winboard/Winboard5.html#[E.7]
http://adamsccpages.blogspot.com/p/computer-chess-utility-programs.html#B
http://www.open-aurec.com/wbforum/viewtopic.php?t=49621
The Winboard Forum link is good, but it's geared to installing UCI engines into Winboard, which is a little different than installing into Chessmaster.
You can make your job a lot easier if you download Alex Guerrero's little utility program called "Polyglot GUI". It somewhat automates the process of adding statements to the Polyglot.ini file.
http://chessprograms.260mb.com/
What is the best engine at this moment? Is it still Rybka 4 or was it beaten?
Thank you so much.