Formula to match lists

[N1k100]

I have a worksheet full of addresses, including postal codes from many towns (approx 40) in two Counties.
I have a worksheet with all postal codes from County A, and one with all postal codes from County B

I need to:
a) match the addresses to which ever County they belong.

b) I then need to know how many people are from each postal code from both County A and County B

Can I get any help with this please. I think its Vlookup but really not sure on these complicated formulas. I am using excel 2003

Thank you in advance

[FDibbins]

a) to match the addresses, you could use vlookup() or index/match

b) to count the names try using countif()

if this doesnt work for you, i would suggest uploading a sample work book for me to look at