Need help with drop-down list

Hello everybody,

First of all, I want to let people know what I am a total n00b in excel, so in case my questions seem like that is because it is.
The reason for registering myself on this forum is to find help to a immediate problem that I have, in the hope that people here will be kind enough to help.

The problem:
I have an excel file with two sheets: Sheet A and Sheet B:
-Sheet B (also named 'Clients List') contains two lists (Names, Addresses)
-Sheet A contains two editable fields: one drop-down list for Names and one editable field for Address

I want to be able to select a name from the Names Drop-down list and the corresponding address to be populated automatically.
If the name does not exist yet, I want to be able to add it automatically by typing it in the drop-down list together with a new address which would be typed in Address field. Must make sure that all new entries have both name and address.


Until now I managed to make a simple dropdown list with names and then I got stuck completely. I can provide more information if needed.

Need help, much appreciated.


EDIT:
I was able to have conditional cell population using the formula

=VLOOKUP(ClientName,'Clients List'!A:B,2,FALSE)

Where ClientName is the cell having the dropbox and 'Clients List' is the sheet containing the "database"

The problem with this is that I need to add new clients and addresses directly in the second sheet (which won't be such a issue after all), as the Address field is populated with the forumla and cannot be edited directly

It would be ideal if I could have the Name and Address field editable and if the data is not already present in the table in second sheet, to be added automatically.