Good luck getting DNS responses from 'root' servers. From what I know, not just any Joe can use them as the primary DNS server for a system. Also, even though you would have a caching local DNS server, every time you would try to get a new site, there would be a performance hit. See, most DNS requests never make it to the root servers because ISP's have their own name servers set up that practically mirror the root servers, and these ISP name servers are normally able to answer your request much quicker simply because they are geographically closer to you (yes, the further away you are from another server, the larger the latency). So in short, it's best to stick with your ISP's nameservers because you can't get to the root servers and it would be a performance hit (unless for some reason you live near one

). If everyone connected to root DNS servers for lookups, the internet would come to a screeching halt.
As for setting up a local DNS server on your machine, you would need bind.
http://ubuntuforums.org/showthread.php?t=236093
http://www.ubuntugeek.com/dns-server...in-ubuntu.html
Search more on google if these aren't for you.
Good luck.