Akkam’s Razor

You have several options for watching TV on your PC.  Here's what I do.

I've had a couple of Hauppauge tuner cards that I've found to be inexpensive, reliable, and full-featured.  You would install one internally in a vacant-PCI slot (ridiculously easy).  You would then install the software, and attach the coaxial cable to the line-in.  With most cable-TV providers, this leaves you with downgraded service (just basic cable, usually no more than 99 channels, and no onscreen channel guide), but for my purposes, that's fine.  You can also attach a cable box, which your PC may be able to control via serial cable, but this will require an additional box as well as an additional fee.

If cracking open your PC isn't an option, there's always a USB TV-tuner.  You can find several here at TrustedReviews, but keep in mind, these are for the UK, which uses the PAL broadcast (versus the US' NTSC). 

The next thing to consider is how you will watch it - will you use the bundled software, a paid third-party application like Snapstream that gives you TIVO-like functionality, a freeware or shareware alternative like MythTV or SageTV, or a version of Microsoft Windows Media Center Edition.  The choice is up to you - if you are buying a new PC, get one with MCE already installed.  If not, consider the other options.  There's also the free alternative from Yahoo by the name of Yahoo Go, which I have no experience, however, it is free.

If you choose to, you can also watch the TV that you are recording from home anywhere on the planet that you have access to an internet connection, including your cellphone, video game console, or any other PC, using free software by the name of ORB (Windows only).

Another choice would be to examine one of the many official and official distribution channels (Techcrunch), from watching TV online straight from the networks on either a free (ABC) or paid (CBS) basis, or via the ubiqtious iTunes.