Something I still dont get about VirtualHosts

Hey everybody,
ok this problem has been bothering me for some time now. I'm hosting a
website at home using a custom dns from dyndns.org.
Now i have dns records for both www.myhostname.com and rasiel.myhostname.com
to both point to my ip address.
What i would like to have is that apache would serve my website only to
www.myhostname.com and not to rasiel.myhostname.com
So here's my question: how do I configure my 'main' server to not be bound
to anything, and to only use my virtualhosts to serve the appropriate
websites to the appropriate addresses?
For the moment i have my main ServerName set to www.myhostname.com and a
virtual host set to the same servername, but even when accessing my website
with rasiel.myhostname.com i get to that website, the only sollution i have
found till now is to add a second virtualhost with servername
rasiel.myhostname.com and to point it to a documentroot that will redirect
it to www.myhostname.com, but i'm sure there must be a cleaner sollution to
this problem, no?
Hope what i said is more or less clear and thanks in advance

TheNavigator