Paypal won't allow free products. Since they make their money as a percentage of sale, they don't allow free products to process through their system. You can build in an alternative checkout for free orders that skips paypal.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.