Data Validation with two criterias

Hi all.. I am just working on a file that was given to me.. Theres basically a menu with a data validation drop down which reads a list.. however the list gets long so what im trying to do is add another drop down above this list
where i should be able to select the reps name .. and den the validation list below it will only show list of accounts for those reps .. what would be the best way to go about this ?? your help is greatly appreciated.. thanks

im attaching a file for example... thanks

When I have wanted to do this, I have used this website as a guide. It is a pretty straight forward walkthrough:

http://www.contextures.com/xlDataVal02.html

dat did the trick .. thanks a ton !!