Need this feature ASAP

I know there is a feature to do this but can't remember how to get it I want to have one listening on that one listing I want to have the option where you can click on a drop-down menu for example click on the size of the hard drive

250GB
160GB
120GB
60GB
20GB

how do I go about this.

Sounds like your trying to set attributes
admin>catalog>attributes controler
:)

But how do I set it up?.

It's okay I worked it out myself.

Got a couple of problems I set them up as checkboxes so for example if very clicked on 250GB £45.00 and 20GB £15.00 and the minimum order was 150 each which would be 300 = £9,000.00 in total I would need each one to be priced differently the 250GB would be £45.00 + 150 = £6,750.00 and the 20GB would be £15.00 + 150 = £2,250.00 can I get it to work like that at the moment it is charging me just for the 250GB even if I click on one of the others and not the 250GB it still chances me for it how do I get it to work like this?.

read this:
https://www.zen-cart.com/tutorials/index.php?article=57

then try this:
http://www.zen-cart.com/index.php?main_page=product_contrib_info&products_id=114
:D