Subdomains and WordPress

I currently have a domain set up with a WP account. I would like to add a few subdomains and not need to log in to 3 or 4 different WP accounts to access them. Is there a way to use the same account for all subdomains, and use a different theme on all of them?

If so, how?

And if not, what can I do? Just have multiple WP accounts?

Thanks!