I have an EL 6cyl, and only on cold starts or when the car has been sitting for a while, i always get engine tapping noise. After about half a minute is runs silent probably because the oil has circulated properly.
Any one with any info as to why this may be? I am assuming it may have something to do with the tappets or their clearances.

Ye, its because the lifters aren't filled with oil yet, if it goes away as you say it does not long after starting, then you're prettymuch spot on with your guess.

Does this mean that they perhaps might need replacing or maybe adjusting?
Is it a big job to replace or adjust them?

it doesnt' mean u need to get them replaced. maybe top up the oil or maybe put a different grade of oil. if the oil is too thin it would sink to the sump quicker instead of staying up the top where the lifters are. thats why on cold starts or when the car has been sitting for a while without being started there isn't enough oil up top until it circulates through the whole engine. but i don't think there is anything to worry about. mine does that too.

its not critical to change them yet... mine started about 10,000 ago, and only now do they tap during normal usage (once temp is normal etc)... so NOW im gonna change them (when i do my cam)... they're fairly cheap to replace from memory