There are a couple of reasons a CD key would not work with Steam. I have a good idea why your specific keys are not working, which I have detailed, down the bottom.
Unsupported Keys: Not all CD keys are intended for use with Steam. There is a pretty good list provided here, which also includes a rough format guide, to identify if a particular key follow the format expected from Steam. This appears to be the main issue you are having, given that neither of the two games are listed as supported.
Dodgy Keys: There have been cases where "dodgy keys" have been included with games. The reason or fault behind each case is irrelevant, but ultimately, it sometimes happens. If the game is still brand new, it would be a good idea to return the game. Contacting Steam, directly, may be the only other was to resolve this particular case.
Outdated Keys: This one appears to be of debate. In theory, all reports suggest that an official Steam key should not expire. I can tell you, however, that not all keys come from Steam. It is entirely possible that a key may simply "expire", at which point, a system like Steam will often reject them.
Used Keys: Use keys are a bigger issue then it implies. Brad Metclaf reports experience with users having simply "brute forced" a key, where a random generator allows users to simply 'keep trying' until their phoney key works. If your unlucky to then recieve this key in a box, it will come up as having previously been used. The older the game, the more plausible, and there have even been cases where companies have mistakingly issued duplicate keys. Your best point of call with cases like this is the company you purchased the game from, or Steam. If the game has been played, before, it is entirely possible that the key has simply been activated already. For this reason, buying key-dependent games second hand is usually discouraged.
Entering the Wrong Key: Always a possibility, so it is important to ensure you are entering the key correctly. You can always try including the spaces and dashes, if you feel this is the only potential differance between what your typing and what is written, but this should not make a differance. To quote the Steam product activation interface,
Please double check to see if you've miss-typed your key. I, L and 1 can look alike, as can V and Y, and 0 and O
Hand-Written Keys: There is further difficulty if the key is hand written. Very unlikely for a legitimate copy, but I have seen it before. If you have a hand written key, it might be worth triple checking those "common appearance" characters. In my experience,
I, L and 1 can look alike, as can V and Y, and 0 and O applies tenfold if the CD Key is handwritten. Please note that a hand written key is a lot more feasible for a legitimate copy of a non-Steam game, where the key is not one use only. For any game where the key can only be used once, being hand written should send up some big warnings that something is wrong.
Ultimately, the games you report trying do not appear to offer CD keys that are accepted by Steam. I did a bit of digging, to find out exactly why either game would come with a CD key. Here is what I turned up:
Spore was released with some pretty heavy digital rights management. It appears the initial use of the game was more restrictive, which of course, was not well recieved by the public. It was credited for bad reviews, and a couple of lawsuits were filed as a direct result of the inclusion. IIRC, the key allowed you access to the game when this DRM was in place. Spore was consequently re-released onto Steam without this DRM, which would explain why Steam does not accept the CD key.
Fable: The Lost Chapters appears to have been released with the initial intention of using the Games for Windows LIVE client. As discussed on the Steam forums, you might be able to register the game through Microsoft for download using their client, however there are reports of issues with a CD Key that appears to follow the same pattern as yours. Ultimately, I believe that if you are having troubles here, and wish to pursue it, your best point of call would be to Microsoft.