Since moving into my current house I've always thought that a centralised media centre would be a great project. With the right tools it can be a relatively low-cost affair that can be set up with very little fuss. The Raspberry Pi is a critical part of this setup, as it allows you to receive or stream through open standards with an incredibly configurable interface.
There are actually 4 components required before creating the solution I was after. I'd need a NAS to store any media, a USB TV tuner so I can watch TV, a powered USB hub (because the TV tuner uses a lot of juice), and (of course) the Raspberry Pi itself.
Before anything, first install RaspBMC onto the SD card for the Raspberry Pi (you can either install this using the download provided by RaspBMC or use the NOOBS distribution).
The NAS is connected to the local network and always on. The Pi is connected to the USB hub and the hub is connected to the TV tuner.
There are now a number of options available to you, depending on which NAS you chose. I used the Synology DS413j, which allows you to set up media sharing through UPnP, NFS or SAMBA. Because I wanted the Pi to cache my media and display it in categories I opted also for mounting the media directories over NFS by adding an fstab entry... easy!
Setting up TV is trickier. In order for the Pi to accept TV it has to be set up as a TvHeadend server (which allows streaming of TV over a network). In my implementation I didn't want to stream over the network, just locally. In either case you need to go to the addons menu and select the RaspBMC settings Addon.
You will need to configure the addon to enable a TVHeadend server and then browse to your Pi using a computer on your network and a web browser. Configure TVHeadend to your needs and then it's back to the Raspberry Pi to install a PVR Addon (from the addons menu) and the last step.
When you configured the TVHeadend server you should also have updated the username and password. Configure your TVHeadend Addon on the Raspberry Pi to use the localhost and the username and password you chose.
And that's it! You can now stream media from the NAS to your Pi, and watch live TV too! If you set up the recording options (as I did) you'll also be able to record either to the Pi or the NAS as well as pausing.