More and more iPad controllers for Ableton are appearing all the time. Conductr is a new offering that claims to stand out from the crowd in that it is specifically designed for live performance. It certainly does have an elegant and intuitive interface that appears well suited to being used live, and despite having one or two limitations, it is generally a pleasure to use.
Initial setup is very straight forward; as with any controller of this type, you can either connect the iPad to your computer over your existing wifi network, or you can create an ad-hoc network yourself that links the two pieces of hardware directly. The makers of Conductr recommend the second method, as the connection should be faster and more stable. They cover the setup of ad-hoc networks in clear step-by-step instructions in the manual and you should be up and running in no time at all.