You can find most walkthroughs and custom strategy guides online. The only strategy guide i use is for World of Warcraft, specifically for raiding dungeons. Gives you tips on how to beat a certain area and a map of the entire dungeon with locations of different things. Also tells you what loot can be dropped from which boss.
I have used walkthroughs before for games but those you find online. I mostly used them for Myst, Riven, Exile...that series. After playing for 4 hours and not getting anywhere it became frustrating.