Yes you can play both Halo: CE and Halo 2 multiplayer on PC.
Halo 2
No. Just like Xbox, you need a Live Account. It should be pretty self explanatory by going to the Microsoft website and clicking on live games.
Not legally.
with a 360 NO. but you can play halo 2 on PC for free
If you have a headset with a microphone, you can talk during multiplayer. You can also type what you want to say.
Yes. but it is hard to come buy you can also get it online but if you do find it dont get surpriced only halo CE and halo 2 is on the pc
Halo CE doesn't have internet capability, unless you have a patch for it. You can only talk on multiplayer if it's local. In Halo 2, that's fixed though.
I don't play Halo 2 on PC but my guess is that if it has campaign or story mode, you can play alone. If you wanna play multiplayer with other players, you can't unless you do local matches.
Yes, Halo 3 can be played in local co-op campaign and in local and online PvP multiplayer.
in campaign you cant but in multiplayer and online you can. go to options and edit your person
Yes, Halo 2 vista is still being played online and has two exclusive maps