stevesh:
I'd be interested in knowing why you want to do this, since many people don't have a 'part 2' to their street addresses (unless you're planning to rename it and use it to collect some other data).
If that's the case, you should be able look at the code that forces the other mandatory fields and add it to that one.
In New Zealand we typically use the following address format
Street Address
Suburb
City
Post code (Same as a Zip code)
We use the suburb field because in some cities we have two streets with the same name.
So I am going to change 'address line 2' to suburb and want to make it compulsory.
Does anone know where I find the code that makes the other fields mandatory?