I fitted our Vista Mediacenter HTPC with a FloppyDTV DVB-C card as planned.
I must say, it sure improves the quality of the picture, especially when stretched to a 100". Using the old analogue tuner, Floor refused to watch soccer, as she couldn't read the score displayed in the upper left or right corner. Now the picture is as sharp as it gets, the DVB-C tuner displays the full mpeg2 stream as obtained from the cable signal. Al tough not sure, Vista Mediacenter probably does some nice interpolation to enhance the picture as well.
The only downsides (caused by the horrible digital TV support of mediacenter) are that teletext is no longer supported and that I needed to sort the 182 channels (not all viewable and this also included radio stations) using mediacenter's channel sort. That's awkward to say the least. But after more than half an hour of continues button pushing, the first 30 channels are in order.