I use XBMC for 95% of all my entertainment, and I tried to cancel my cable. Unfortunately I watch a lot of sports and it is untenable most the year. There are just too few options, and those there are are extremely limited.
Basketball, baseball and hockey are the worst. Local teams are no longer on OTA cable at all (except for some baseball). Even the Stanley Cup, the ALCS, and most of the NBA playoffs are cable only now.
You can subscribe to MLB.tv and NBA League Pass, or the NHL equivalents but:
- All have black out restrictions which make watching the local team impossible without cable, due to agreements signed with the regional afilliates
I'm in the SF Bay Area and cannot watching any of the local teams (Warriors, Giants, A's or Sharks) with the legit options.
If your dad is a fan of the out of town team you might have better luck. My buddy moved here from Michigan and can watch the Tigers, Pistons, or Red Wings using the above services with no problem.
- The subscription fee for all three services is comparable to the monthly fee for cable + HD + a sports package
Football is a little better with an antenna and the ESPN 360 package (on Xbox 360, no decent plug-in for Boxee or XBMC yet). You can see the same NFL games on Sunday with Antenna (minus Red Zone) and it looks much better than over any cable provider. You'll miss the six or seven NFL network games and all Monday Night Football. You can also see most top 25 College games either OTA or on ESPN 360. You will probably not be able to see the local FBS college team, again due to deals with cable affiliates.
International soccer is okay with ESPN 360 (all World Cup games were on there). If you're a soccer fan you're probably used to watching it less than live already so the delay is not bad. You can usually find torrents for anything in Europe by the time you get home from work (the Classico is on my hard drive right now). It doesn't sound like your dad is much of a international soccer guy.
I'm a big boxing fan and there is no way to see HBO or Showtime fights without a subscription (except illegal streams). I have no idea what your MMA options are, but I think it is the easiest thing to find illegal streams of.
College basketball is worse than anything else during the season, but March Madness is on CBS and cbssports.com, so you can watch every game with an HTPC and a web browser and an antenna.
The long and short of it is sports on an HTPC is just not ready for prime time. The only real solution is using something like Justin.TV or other non-Us streaming sites and these are unreliable, look poor, and difficult to track down for 90% of sports (ie, anything but soccer or NHL.) There is no way a non-tech saavy person could find a game on Justin.TV using the Boxee or XBMC plug-ins.