Does it matter whether they're free or commercial GUIs?
I don't know what ChessNetwork uses, but some of the better free GUIs are (in no particular order):
1) Winboard 4.7.2 - http://www.open-aurec.com/wbforum/viewtopic.php?f=19&t=51528
2) Arena 3.0 (My favorite, but some prefer other GUIs) - http://www.playwitharena.com/
3) Scid vs. PC 4.10 - http://scidvspc.sourceforge.net/index.html
4) Scid 4.4 - http://scid.sourceforge.net/
5) ChessX 1.0.0 (Only for analysis and database work - Doesn't play games) - http://chessx.sourceforge.net/
6) ChessPad 2.0.3 - http://www.wmlsoftware.com/chesspad2.html
7) Tarrasch Chess GUI 2.02ar (very basic, but easy to use) - http://www.triplehappy.com/
Maybe others I can't think of?
OK, rooperi suggests the Stockfish engine - http://stockfishchess.org/
The Houdini 1.5a engine is also popular - http://www.cruxis.com/download/Houdini_15a.zip
There are many other free engines that are good.
Can you guys suggest any Chess computer programs like those alpha-style ones I see where you can analyze? Like the ones used by the ChessNetwork; or something better? Please?
Thank you.