I found this app and it is great for use with a carputer.
http://www.mobileairmouse.com/
I've seen other iPhone remotes and was not impressed with them. This one works well and has some very nice features such as touchpad, full keyboard, media player and web controls, and the ability to create shortcuts. The air mouse works too but I prefer the touch pad.
The only down side I have found is that my iPhone loses its wifi connection when the PC connects to my wireless N router, but it will work when the PC is connected to the G router.