Advise required in relating two lists

[Neeraj]

I have a database of around 90000 addressess of which 30%
donot have zipcodes. Also I have a separate comprehensive
list of zipcodes and which areas fall in which zipcode. I
want to explore the possibilty of automating the process
of putting zipcodes in the addresses. I was thinking of
using a complex series of functions (vlookup, index, match
etc.) or some sort of join operations between the two
lists or some sort of VBA procedure. Please advise on the
approach/technique which can be possibly used to achieve
this aim.

Thanks and Regards

Neeraj