Hi plshelp,
There are two answers to this question: what the law says and what actually happens in practice.
Because the graphics, music and sound effects in a game are all separate copyright works, a user who 'copies' them in a walkthrough would infringe those rights if the amount copied was substantial and was not permitted by one or more of the exceptions I mentioned in the other thread. Measuring substantiality is notoriously difficult, but generally the court will look at whether the essence of the copyright work has been copied. I think that unless it was a fairly trivial (and therefore pretty useless) walkthroough, it is bound to use a substantial part of the game. If the purpose of the walkthrough can be be described as a review of the game (your guess is as good as mine whether this argument would hold water), then section 30 might apply. Equally if a walkthrough could justifiably be termed 'quoting' then again that amended part of section 30 for quotation could apply. But with both of these exceptions, the key words are fair dealing, and I don't think that an extensive walkthrough of a game would meet this criterion. That said, I am not aware of any court cases on this particular aspect, so we just don't know.
That's the legal position.
However in practice it appears that some games manufacturers are prepared to turn a blind eye, while others are not. A couple of years ago there was quite a flurry of takedowns of unauthorised walkthroughs posted on YouTube, and in most cases as far as we know none of these were tested by the courts either here or in the USA. Takedowns are effectively an easy option for sites like YouTube to avoid liability for infringement, and they don't always have a good legal basis. I would suggest that, irrespective of the strength or otherwise of your legal position, it is the attitude of the games manufacturers which will determine how viable your project is. The upside is that if you publish a walkthrough and the game's manufacturer objects, the most likely outcome is that they will ask for it to be taken down and if you don't fight it, that's the worst that will happen. Fighting a takedown notice, especially if the manufacturer isn't based in the UK, could be really expensive.
Sorry that I can't give you a clearer answer. If you would like another take on this subject, see this posting by a UK lawyer who specialises in this area of law:
Gamerlaw