Which free engine and GUI?

I'm currently using Arena 3.0 and Houdini 1.5 on Win7 (32bit).

However for some odd reason, I can't fully intall Arena,  and I have to keep running it off the zip file, and thus have to keep installing Houdini again (this is everytime I want to use it, which as you can guess, a bit of a pain).

What other alternatives are there? I don't need the strongest engine (yet), I'd like a nice GUI, which is easy to use etc. I'm mainly looking to play against the computer and to analyse games.

Thanks and regards,

m12

p.s. url links would be really helpful. 

Ok scrap that, I finally got to work. I'll play about with it more.

However the question still stands, is there anything better than Arena and Houdini 1.5/Rybka 2.2?

Stockfish is fast but not as strong as Houdini:

http://www.chess.com/download/view/strongest-open-source-engine

Houdini and SCID.  SCID is fantastic.

Houdini, Stockfish and Firebird are great free chess engines, any decent program should be able to handle all 3 - BUT only one at a time of course :) And to be honest you don't need anything better than what you already have (neither do I, and I have everything I'm recommending inc. F12) but it wouldn't hurt to have more engines with different features/options/playing styles.

Offhand I can't think of a good free chess program because I'm out of the loop here but if you're not totally broke look around for something like Fritz 10 or 11 at eBay and amazon (or even here) as they're up to F13 now so you should be able to get a real good deal on a new (ie never used) older version. And in most cases even a used version should be OK as long as you're dealing with a reliable seller. Depending on where you live maybe you can look around for older versions of Fritz, ChessMaster or other reputable programs in "bargain bins" at dept and PC stores. These programs are worth the money if you have time to use them because they include lessons, tutorials and lots of options for how the engine runs (ie how much time it spends per move or game, the depth of ply search, etc) and the engines that come with these programs are also excellent at least for anyone below FM/NM strength.

Thank you for the replies.

Nimzo, I already own Chessmaster GM ed, which more than serves its purpose, it really is a fantastic programme.

I'm holding out get any of the latest ed of Frits, Rybka et al because IIRC the PC ed cannot be installed on a mac (I'll be getting one shortly )