Supposedly subdomains are treated as separate sites, are indexed separately, and do not pass PR.
The KEY is to NOT link from the root domain to the subdomain. You do NOT want two way links, but you want to be able to push traffic from sub to root, if that is your plan.
Now if you are just testing, don't link either way, and you're supposed to be golden. The sub can be slapped, but the root is supposed to get away without injury.
