Should I get Civilization 4 or 5 or both?

[Bane]

Haha yeah they're only about a tenner I think..

No I haven't played 1, 2 or 3...

Should I?

You might as well try a demo of each and see which you prefer.

Unless you understand the game intricacies and enjoy trying different strategies then the series mightn't be for you. And Civ 5 is meant to be the easier out of the two.