Don't worry about the cheating part - I've actually got the strategy guide for LOZ

H, without it I would barely have made it past the first dungeon
I agree that Mario and Luigi: Partners in time is another good, similar rpg. If you want a real challenge though, Final Fantasy IV is out next month, or pick up one of the older FF DS titles.
In terms of quality DS games (aside from the obvious New Super Mario Bros, Animal Crossing etc), Soul Bubbles which was out recently is great and so are the Pokemon games and if you want something a bit different Elite Beat Agents and the Phoenix Wright games are worth trying. Also, I personally can't wait for the release of Professor Layton and the Curious Villiage which looks really interesting!