Vlookup to autocomplete monthly report

Hi all,

Attached is a sample of what i'm working with, so please use/edit.

I want the report to be self compiling once you select a client and a month from the two drop down lists.

However;

1) i'm not sure the best way to arrange the data for Vlookup to work
2) how to link the drop down lists to run the the correct Vlookup formula

any help would be greatly appreciate.

Dan