You ask a highly subjective question. What I consider difficult might be simple to you and vise versa.
As far as I know, you need an actual TV tuner card in order to use the TV functions. Unless you have an All-In-Wonder or VIVO video card which has a TV tuner chip integrated in with the rest.
Might not be what you're looking for, but I'm in the process of creating an Xbox Media Center device. I just picked up a used Xbox for about $150 and a DuoX2 modchip for about $25. A little soldering, and I'll have myself around a $200 box that can do just about everything Windows Media Center can and more.
How difficult is it to use as a DVR? And also, is it necessary to have a TV tuner for the PC, or could it just work by connecting through an S-Video cable?