You don't need to base it on Linux mate, there are plenty of cards and apps that run under Windows and they are much more user friendly than the Linux ones IMO, search for RitzDVB, MyTheatre, MultiDec, ProgDVB etc, they are very easy to setup and run, I used to run My Theatre on an old Celeron 400Mhz with 128mb of RAM, using a Technotrend 2.1 card, this had a hardware mpeg2 decoder so it did all the processing onboard, if you use a budget card without a built in hardware decoder then you'll probably need a higher spec machine to run it.
Linux setups tend to require less CPU power and offer more features, but I always found the Windows solutions more than enough for my needs.