Just to add a slight clarification to Gizmo's input,
Patents are all about the claims when you are seeking to determine whether or not you would be infringing another patent.
The claims do not actually matter if you are simply seeking to determine whether or not your invention would likely be patentable.
For it to be patentable, your invention must be "novel" (not done before) and "non-obvious" (sufficiently inventive, for the most part) in light of any prior art. Also, any available patent protection will, for the most part, be limited to the individual aspects of your invention that are novel and non-obvious. Prior art does not have to refer to a patent, either, it can refer to anything.