Assuming your DNS provider is doing all the right things, you have a number of options. In all cases, the real Apache documentation on virtual hosting is best.
In your case, the simplest way to deal with this is a simple name based host:
The simple example provided is generally adequate. What I have done with XAMPP is create a new HTDOCS area for my public websites and only allowed localhost access to XAMPP pages.
You can also do completely dynamic Vhosting if you have alot of potential domains. Apache has an excellent page detailing all the various methods: