Recently I've been shopping around for slightly older NON-STEAM PC titles. Amazon and Ebay specifically have cheap PC games......that are used. The questions that struck me is: Do the CD-keys of these games really matter for registration to play the game? Or are the keys just for the CDs themselves, that once you enter the key, you can play the game with all its features offline AND online. For example, my Warcraft II disc does have a CD-key, but does not need to be registered online, and thus that key is not bound to any one owner. Would you trust buying a used PC game, assuming CD-key included?  
 
If you guys have any knowledge about whether a used copy would work and if these will run on a modern system (windows 7 x64), some info would help. Piracy is not an option here. 
 
USED PC Games I'm shopping for: 
 
 Quake 4 -I do not have a 360. 
Legacy of Kain Series (all 5 games) -I want higher resolutions with the PC. PS1 and PS2 versions just do not look as good. 
 Diablo 1 -never played it
Warcraft: Orcs and Humans -never played it  
Medal of Honor 10th Anniversary
Battlefield 2142 -not on Steam strangely, yet Battlefield 2 is.  
Halo 1 -never played it. I'll need to buy Halo 2 new for GFWL, but how about Halo 1? 
Fable 1 
Resident Evil 4  
 
That's all I'm looking at for now. I know GOG has some good older titles as well, but I don't think any of those are on there. 
 
Note: It's messed up how some people are selling used copies of retail versions of Steam games, WoW and its expansions, etc... 

I have a hard time understanding your post but the games will simply not install without their CD keys. You'll also have a hard time finding used PC games i believe.

Just make sure it doesn't have securerom DRM and yes you need the cd key for all these games. Some of these are old, so it might not need to register online. Eb games doesn't sell used pc games anymore and it's usually not a good idea to buy it because of these things.

" I have a hard time understanding your post but the games will simply not install without their CD keys. You'll also have a hard time finding used PC games i believe. "

If the game forces online registration (and ties the CD key to your account), then you're screwed and can't get it. If someone already used the key, selling it on second hand is the same as selling someone a car without the keys. 
 
However, that's more of a recent thing so nearly all the games on your list should be fine - the CD Key is random and merely used to allow you to access the installer, nothing else.

They're all old and most likely cheap to get new.

just to clear things up. I am not asking if I can buy a used PC game without the CD-key. I am asking if I can buy a used PC game WITH the CD-key and if that CD-key would work.

With these games you should be able to enter the CD key as many times as you want, it might not work online if the code is in use though.
 
I would think.

I don't think Battlefield 2142 will work though, I think it's bound to an account. 

Battlefield 2142 and Quake 4 are the only ones I forsee problems with. BF2142 I think it's almost guaranteed to have some issue, and Q4 depends entirely on what DRM is used. Many of the other games on your list will require CD keys, but the only restrictions they'll have involve online play; you can install the games on a million different computers, but you can only play online--as in multiplayer--with one at a time.

" just to clear things up. I am not asking if I can buy a used PC game without the CD-key. I am asking if I can buy a used PC game WITH the CD-key and if that CD-key would work. "