I've been playing with the most recent version of Mediaportal and find it streams the FTA SD channels nicely on my wireless network to laptops around the house.
Sadly no
Sky pay channels will decode (including my beloved RTE 1, RTE 2 and TG 4) as my Irish
Sky sub has switched to the white card. I can decode the white card in a Technomate TM-6800 super (but presumably the card wont auto update) and the Technomate doesn't offer a PC streaming service - though with the Ethernet port on the box it could if someone programmed it to...