cmwblog on "WPMU cart help"

I have set up WPMU and it works great. I need to find a way to centralized cart for each blog that will be on a subdomain and to be able to track through some type of affiliate tracking.

My first thought was to have something like oscommerce on a separate install and call in the products from WP and somehow attach the affiliate link so that the blog that sold the product can be tracked.

Any suggestions?

thanks,

PG