It says that $zipcode requires explicit package name. Not exactly sure what that means....
And I would learn some XML, but homework, mostly, keeps me from that =(
That error means that you are using strict (which is good) and you didn't declare $zipcode with my. If $zipcode is a global variable then put my $zipcode; at the top of your program somewhere. If its in a sub then put my $zipcode; in the sub somewhere before you use it or when you assign it (my $zipcode = ....)