product restrictions

[MoniqueCordes]

Hey all

I'm new to VirtueMart.  I would like to know if the following is possible, and if so, how do I go about it.

I run a store that builds custom bicycle wheels.  There are 4 product categories to the store (the 4 parts that make up a wheel ie rims, hubs, spokes and nipples)  A customer needs to purchase an item from each of the 4 categories before they can check out.  How do I ensure that the customer added one of each of the parts to his cart before doing payment?

Thanks!