drop down box

I've been reading on this and I still can't figure out how to do it. I want to have a drop down box that can calapse when you select an option. I'll tell you my example that I need:

I have a material column, underneath material I want to be able to choose from a variety of wood species. Like this:

MATERIAL
(PULL DOWN MENU WHERE I CLICK ON AN ARROW)
RED OAK
W. OAK
HICKORY
A. CHERRY
B. CHERRY....ETC.....

I've attached a zipped file of my spreadsheet incase you all wanted to see what I was talking about. I'm brand new to excel so go easy on the design of my spreadsheet .

1) Select a column. Column A for example
2) Call it materal
3) Type in your list of the different material
4) in cells A2 to A4 type in the values listed below
POPLAR
RED OAK
BIRCH PLY

5) Select a cloumn where you like the drop down list
6) Select the range B2:B15
7)Click Data-->validation
8) Under the setting tab you will see a dropdown list under the word Allow
9) Click on dropdown list and select list
10) click on the button at the right side of the filed under the word source
12) select range A2:A4 and click ok
13) if you click on cell on any cell from B2 - B15 you will get the drop down list

Oh wow...man this is some really cool stuff! Thanks to both of you, all the info helped me out and I know what I was doing wrong. I got the valdiation part but I couldn't figure out why the drop down box didnt appear. All I got was a tan colored box where I had my values.

Thanks again!