Create an add or upgrades menu or facility?

I am developing a computer sales site and have the products on board. What I would like to be able to offer customers is the ability to look at a given product and be able to chose additions or upgrades to the product so that the core product and additions/upgrades are added together or listed together when the purchase is finalized and the checkout button is clicked.

example:
customer looks to buy a Dell Optiplex GX123 512mg ram 40 gig Hard drive for $100. but can also opt to upgrade to 2 gig ram for $60 and upgrade to 80 gig drive for $25.

I have looked through the forum and can't easily find the subject, but I am sure it must have been discussed.

Any ideas ....[FONT="Arial"]

Regards

Use attributes..tutorials/faq top right of this page
OR
PC Configurator mod from
http://www.zen-cart.com/index.php?main_page=product_contrib_info&products_id=667

Thanks for the response.

I did a bit more research and attributes seems to be the way to go.

I should have researched a bit harder before posting.

RTFM ! comes to mind ................
http://www.zen-cart.com/forum/images/smilies/oops.gif