Is there something which may:
- Play music, at the very least in MP3-format
- Play video in various codec’s
- Helps in recording video of shows from TV through a TV-in card
- Helps in organizing music and videos
- Works with a keyboard and mouse
Additional pluses are:
- If it also is possible to browse the web through it, or at least start the web browser
- Has some games. Maybe through MAME or some other emulation like SNES or something.
- If it’s also possible to control it through a game pad.
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.
XBMC (the software formerly known as Xbox Media Center) can do most of your requirements except for the recording.
MediaPortal is it’s bigger and slightly wonkier relative, it can do recording but is in my opinion a bit trickier to set up.
MediaPortal has been my best choice so far, and has worked well for most all of my uses. Unlike some of the other responses, I found it fairly easily to set up and almost negligible to maintain. I primarily use it to watch recorded or downloaded TV shows and movies, and it works like a charm.