"Media Poral got plugins, one where it's possible to start other apps, like browser, emulator/games etc. Can do (i think all) your reqeirments and maybe more. Can also handle timeshifting (right word?) and pause the tv-program you are watching etc.
As grapefrukt mentiond it's not trivial to setup, but probably what you are looking for."
"I've used Tversity. I don't think it allows TV recording, but it excels at transcoding on-the-fly and streaming to UPnP AV/DLNA devices. Then there's XBMC, and Boxee (an XBMC fork).
Look through this Lifehacker article for a roundup of media centre options. There's a separate roundup of DVR applications for your TV-watching needs, with some apps featuring in both lists."
