add bundle products to shopping cart at once

anyone know if their is a way to bundle two products together. if one gets placed in the shopping cart then the other one should automatically get added as well. if one gets removed from cart then the other one should get removed as well.

pricing remains the same for both just they either have to be both bought or none.

Create a separate product for the bundle with its own id and use a backend ERP system to create "bills of materials" and manage stock. Zen Cart can remain agnostic about the ingredients of the product. (I'm a little biased. I think that a lot of these shopping cart programs ought to be reduced to core functions and leave inventory management and order processing to other programs. Maybe this could be discussed at the big open source software convention this weekend).

Yeah, I looking for this feature in Zen Cart but I can't found it yet.
I sell downloadable product and in my old store (no zen cart) I had a simple way to add combos or bundles... now with Zen Cart I can't!