Namecoin in itself is a peer-to-peer DNS system based off of the Bitcoin code. You use Namecoins to register your own domain, though at the moment you need a custom DNS server in order to resolve those .bit domains. Useful for the same reason Bitcoin's decentralization is useful, namely, that these domains can't be blocked by a governmental authority. The project is still in its infancy right now though.
Bitparking I have no idea.
You will always need a DNS server to resolve an host, i miss the point in this. The custom DNS can be easily blocked and i don't think anyone will fell the need of installing a program just to resolve some .biz domains.
The "untraceable" nature of bitcoins is lost in this project: IP addresses are associated to a company/person and they can be very easily blocked.
It's a nice concept, but i can't see anything more than that.