Since a PC system is just a collection of individual components brought together, there's no reason why one of those components can't be a combined keyboard and trackpad, like one of these: http://www.kustompcs.co.uk/acatalog/info_3003. html
I love my trackpad as it has two finger scrolling and one touch clicking, or whatever it's called. I now never have to expend the effort to manually "click" - before I had this laptop I hated trackpads and always used a mouse...