So you want to use one device to control another device when they're both on your person? I have trouble grasping the value, but - in any case, I don't know of a straightforward way to do this. I imagine there's a client that will do it via bluetooth.
As far as controlling a remote computer with an iPad, lots of ways to do this ... I tried LogMeIn tonight for the first time. Works great. It's easy to set up in minutes. But it does require the host computer to be awake and connected to the Internet.