I'm using a DigitalNow TwinDVB-T Receiver and it works brilliantly in MCE 2005. I believe other people on the forums have got them working on Vista using the standard drivers as well (wife won't let me try Vista on the main MCE box, so I've got one of the external TinyUSB DVB-T tuners on order to try with Vista as it uses the same drivers).
DigitalNow TwinDVB-T Receiver
As long as you have a free USB header on the motherboard of your PC it's simple to install. And they work fine with HD TV (I use it for streaming to an XBox 360 hooked up to the LCD TV in the lounge room).