Vista is on the out. Microsoft has extended XP and will add DirectX 10 to the next SP. To get the true benifits of Vista you need the 64 bit but the problem with that is most all hardware venders are not going to waste their time making drivers for a OS that is not in Demand. Vista has alot of issues and only time will tell.
Andy for most TV cards to work they have to be certified. HP has always had issues with Media center all the way back to MCE 2004. I have a nice PCI express TV turner It is true HD ATSC
http://www.avermedia.com/. You can get it at tigerdirect or newegg for less than $100.