Get a Hauppauge WinTV Nova HD S2. That's what I use and it works flawlessly. However, one big warning! Avoid ATI graphics cards with BBC HD. Basically, they don't work reliably. Depending on who you want to believe, BBC encoding, ATI chipset/drivers or Microsoft's decoder or some combination of them are the source of the problem. Nvidia cards do work without a problem and you really do need a relatively recent discrete graphics card. Older cards may not cope at all and on-board graphics (if they work) will have your CPU (and the fan attached to its heatsink) running flat out at times. I use a fanless Nvidia G210. They're cheap and have 6 channel audio out over HDMI (no need for a connection to SPDIF on your Motherboard or sound card).
The original 32 bit junkie now snorting pure 64. BT Yeehaw! 8 Mbit BT Homehub2, Wired, Wireless, VoIP, 2 Macs, 2.5 Hackintoshes, 3.5 PCs, OS X, Win XP, MCE, Vista, Ubuntu.
Rehab is for quitters