you can get some of the best tutorials online - just google it . a book is fine (whsmith usually have one that is published for themselves for about 15-20 quid) but quite limited sometimes they dont start from the basics and skip steps that they assume you will know - the benefit to online resources is the variation - you may get four or five completely different tutorials which all create the same result - the advantage to this is that you find a way to do a certain thing that suits you better than another the following are a couple of links to good sites with free tutorials (never pay to use tutorial sites there are more than enough free ones and i would question any sites that ask for paid membershipbefore you can view tutorials )
Photoshop Tutorials / Good-Tutorials
Computer Arts - Tutorials
the second link is for a magazine that you can get in whsmith's but costs £7 - you dont really get anything from the mag that you cant get from the site for free!!