There are three different versions " . "  
 
Two friends and I are planning on getting SCII, but all of us are noobs to the series and are wondering the following: 
1.) Can you play between all three versions?
2.) Is one version clearly better than the other two? 
3.) How many players can play at once (is there three way battles?) 
 
Thanks in advance!

Well it's gonna be three releases, but there will only be one out when the game first launches: Wings of Liberty.  
 
I bet the expansions (if you could call them that) will work with multiplayer similarly to Brood War, you can play the original with your friends.

Yea, Think of it more like a base game and two expansions, not three different versions. 
 
 
And if you do want to become better, go to Teamliquid.net , A HUGE wealth of resources for both BW and Sc2. (I suggest the Day[9] dailys)

To answer your 3rd question, you can play up to 4v4 online, although for those of us in the beta at the moment its limited to 1v1 and 2v2.

1.  As far as I know, it's still unclear exactly how all 3 versions will interact (3 stand-alone games?  1 full game and 2 expansions?).  But what is certain is that everyone who owns Wings of Liberty will be able to play with everyone else who owns Wings of Liberty, so that's a baseline guarantee.
2.  Not clearly.  If Wings of Liberty turns out to be a stand-alone game with the other two games as expansion packs, then Wings of Liberty will be what you want to get to start with.
3.  Very likely 8, like in the original StarCraft.  I see no reason why 3-way battles wouldn't be entirely do-able.

You should most definitely get Soul Calibur 2 :P 
The three games format isn't set in stone as far as the general public knows, but I am inclined to believe that they will be three stand alone games with some sort of benefit to people that buy all three.  
It's too early to know whether one is better than the others.  
3 players is certainly possible.

1.)There will only be 1 version with two expansion packs. It's not like its Pokemon Red/Blue. The expansion packs will be as long as the Wings of Liberty campaign is. Along with some multiplayer improvements.
2.) No. Buy Wings of Liberty and if you like it buy the expansions.
3.) Up to 8 players can play at a time.