Virtual Directories in IIS

OK so I have a site called

www.mysite.org

Now I have it set to d:\inetpub\mysite

Underneath that i have a folder called \branches
with subfolders for cities

ex d:\inetpub\mysite\branches\lasvegas
d:\inetpub\mysite\branches\lasangelese

Now how do I get it to view like this with my current folder tree

http://www.mysite.org/lasvegas

I dont want to make a virtual folder for ALL branches .. thats like 40 virtual folders .. dont want to do that I just want one virutal folder that will then just make it available like so

http://www.mysite.org/lasvegas
http://www.mysite.org/lasangelese


thanks for any info you can provide me.