Not sure what you mean by "register", but...
www.site.com is just a sub-domain of site.com
Regarding domain registration, if you own site.com, you also own
www.site.com, sales.site.com, customers.site.com, etc, etc.
As far as adding sub-domains, that is up to your web host.
Cheers
(ETA)
Most web hosts treat
www.site.com and site.com as an alias, I believe. But you could have a completely different web site at both. (confused yet? I am...)
[quote author=Hollow_DiMM link=topic=8296.msg45968#msg45968 date=1173196815]
Does anyone know how to register their site such as:
http://www.yoursite.com
so it also is registered as:
http://yoursite.com
[/quote]
You wouldn't need to pay again. Most web hosts set up sites so they can be reached by either
www.yoursite.com or yoursite.com but some lazy hosts only set up
www.yoursite.com.
Thnx Peeps 