dropdown comparisons

I have 2 dynamically created dropdown lists which are regions and officers.

i wish to compare the region selected to the region the officer is assigned to (onChange of officer), and if the region is not the same as the officer region then throw a warning...

Basically HOW do i capture the contents of the rs's chosen in the dropdowns  to compare them?

tbl_regions: id;region_name;active_indr;

tbl_officerinfo: id;officer_lname;officer_fname;officer_region;

yes yes... more so the coding... i understand the idea

I just have no idea about the code!

thanks though