One warning: my next door neighbour bought an all-singing PC with Windows Media Center (sic). She couldn't get TV or much else to work on it, and after lots of (very rude) 0870 helpdesk, asked me to take a look.
It turned out that her particular supplier didn't include CODECs (you had to buy them separately) or a "remote controller". Apparently, you can't do everything from the keyboard - at some point, it demands that you have a TV-like remote control, and will go no further until you do.
I got her the relevant leads and stuff, installed the CODECs, and it can now do most of the things she wanted, but she isn't impressed with how slow it is to change channel, and what a faff it is to record to DVD (you have to record to HD, then copy to DVD). Her TV set in the same room changes instantly, and her separate DVD recorder "just works".
The Media Centre PC is relegated to the conservatory for the children, who are mighty impressed with this. She's planning now to convert the garage to a "children's room" to recover her conservatory from the hordes of teenagers playing games on the Media Center.