Fable games are good, at best. Certainly nothing amazing. They were supposed to be the end-all be-all of emergent gameplay, with every player action changing the plot in meaningful ways. As it is, it's basically a fairly linear, standard action game with a few time-based gimmicks. The art is nice, I will say that much. Very little else stands out, though. Characters are bland, plots are utterly forgettable, sidequests are mostly routine fare, blah blah blah.

Anyway, to specifically answer your questions:

1) Yes, it's worth getting into the series even though you can't play the middle part, but only if you don't have anything better to play. It's decent fun, but definitely not a "can't miss" series.

2) No, you won't miss out on anything important. A few fan-service references is about it. The games are set in the same world but the plots are very different and you'll have no trouble transitioning from I to III.

3) No, there's no way to get a 360 game running on a pc. Trust me, it can't be done. Just borrow a friend's 360 for a week or so if you must play Fable II. Again, though, probably not worth it.