I'd been making our company's install programs for quite some time when I stumbled upon this book - and I must say my life would have been a lot easier if I had known about it months before.
I happen to think that the Installshield web site and help files are quite good, if you have a good idea of exactly what you are looking for. When you're not sure however it can be difficult to find the right information.
This is one of the areas where the book is great - giving overviews, sample code and explanations of why you should do certain things in a certain way.
If you have someone at your place of work just starting off with InstallShield make sure you buy them this book it will save them a whole lot of grief. If you're already familiar with the product then I'd still recommend it as it will probably show you a few things you hadn't thought of.
(Although the book is aimed at InstallShield 5.1, the author is going to release another chapter on the web for version 5.5 When its up you can look at it here