Proving a pair of integers are not prime in a particular number system

Basically i've been given a number system G defined as follows, numbers in G are ordered pairs of integers i.e. (a,b)\inG if a\inZ and b\inZ. Z is the set of all integers. Addition and multiplication are defined for G as follows

(a,b) + (c,d) = (a+c,b+d)

(a,b) x (c,d) = (ac-bd,ad+bc)

I have to show that (2,0) is not prime in G even though 2 is prime in Z. I'm then asked to find two factors of (2,0) that aren't units.

I've been stuck on this question for ages now and i've had no luck with it. My lecture notes havn't helped too much. Any help would be really appreciated.

Thanks, Mark