What type of a monitor? Just a simple one with one DSUB 15-pin connector and/or one DVI-I/-D connector?
You have to have at least a HDTV tuner installed on a PC powerful enough to display up to 1920*1080 video. It'd better have at least 4GHz Pentium 4 CPU (not the clock speed, but the power) and one of the latest graphic cards. Most modern CPUs from either Intel or AMD and most modern PCI Express graphic cards from either ATI or NVidia would do. I'm not sure of the new Intel GMA950 built into the 945G chipset.
From my latest search, the cheapest PCI HDTV tuner costs US$50 in South Korea, one of the Dvico Fusion HDTV 3 series. What I myself have are Fusion HDTV 1 and one hardware-based PCI card. Since HDTV tuners by now are very cheap compared to PDP and LCD HDTVs, I'd like to recommend spending some more to have one of the latest HDTV cards. Can't cost over $100 or $150.