I have never played a Civ game in my life, so i thought i ought to get the complete pack while it was on the cheap on steam. 
 
So i now own 4 different versions of Civilisation 4 and i have no idea which i am supposed to play. Are they all different or is the latest the best and i should just stick to that. 
 
Any advice would be much appreciated

civ 4

My understanding is that you should play Beyond the Sword, as it includes everything from Warlords except the scenarios. Colonization is sort of like a mod, so play that if you get bored w/ the original. 
 
I just got the pack, too. I remember play a bit of Civ2 way back when, but the interface of Civ4 is confusing the hell out of me. I really have no idea what I'm supposed to do. How do I establish trade routes with other nations? Are there other forms of diplomacy other than "Open Borders"? Can someone please help me?

Play BTS, and Colonization is just a remake of the old colonization made in the early 90's or something

My cousin is thinking about buying it...is it any good?

Civ4 is very good once if you have a thing for old-school 4x gameplay. I still sit down to play Civ4 every once and a while (though honestly I prefer the setup of Empire: TW more than Civ, but that's just personal preference)

I'm in the same boat (about to purchase) Is it worth buying all of the parts or should I just buy one of the games?

buy it all it like 4 dollars more expensive 
civ 4 is the best and u get the two expansions with it, but u have to learn it, play the tutorial, fight against ai 
 
this aint no mw2...

" buy it all it like 4 dollars more expensive civ 4 is the best and u get the two expansions with it, but u have to learn it, play the tutorial, fight against ai  this aint no mw2... "

cool thanks for the help so start with the original and move onto Beyond the Sword and then colonization when i get bored.

" cool thanks for the help so start with the original and move onto Beyond the Sword and then colonization when i get bored. "

I doubt my computer can run Civ IV, but I did buy Civ 3 Complete for $1.25. Even though I'm not a huge fan of Civ. Yes I am a sucker. 

I never played the expansions, but I found Civ 4 to be quite addictive. I would say if you could find it, play Civ 2 as I found it was easier to get into and less complicated. I would also recommend building several cities when you play. Taxation isn't so heavy in the early game so if you can irrigate as much as possible before it does you could kicks up with a financial head start.(at least this strategy has worked for me)