Channeling Emily Post on facebook

I'm not exactly the socially savvy cool person, but I do make an effort to follow social convention when possible. That can be troublesome.. because I don't always know what kind of response a situation calls for. I've got the whole ex-boyfriend-of-my-best-friend-who-pets-my-head-in-bio-class thing down, but there are certain situations (occupational hazards of being nerdy) that don't come with a manual.
What do you say to the kid who's the arch enemy (?) of someone from your school (who used to be a friend of yours, but is now extremely conceited, also your "boss" at the school paper). It's not over a girl.. or a sports rivalry.. It's a science competition thing-- and not a petty one. Red head from the other school was top 5 nationally in Intel and the one from your school won 2nd place psychology award @ international science & engineering fair... and they had a "showdown" at a local science fair. They hate one another passionately, but, uh, I had to see both of them every week last year. separately, but still, don't shoot the messenger!
Anyway, now that school is over I'm spending a lot of time on facebook until i start doing something useful and I've noticed that I"m bypassing a lot of birthdays because I don't know if it's appropriate for me to "care." And everytime I'm invited to a party I sort of wonder if I should rsvp, because what if they invited me by accident? (I've done that before.. those buttons press themselves, i swear!) Can I like that person's status? It's funny, but I don't talk to them-- wouldn't want to be a creeper!
It's nice, in a way, that fb offers a little window into the social life of people I normally wouldn't know anything about. It's interesting, it gives me the illusion taht I actually know them. Of course, sometimes I forget that it's really not a "substitute" for actually knowing them. That becomes painfully obvious when I talk to them and realize.. oh. they never told me that. i should probably pretend i don't know where they live. i can do things on fb that aren't acceptable in real life and vice versa, but no one offered a social guide to facebook that outlines the specific instances in which this is true. sometimes privacy settings take care of that for me, which is a relief, but then there's the whole fb chat thing-- is it really creepy to talk to people that way? I use it all the time.. mostly because I don't want people to talk to me.
Oh, well, I guess that sort of defeats the purpose then....