You will need to edit the apache config file.
What you are looking for is called, 'virtualhosts'
Example code looks like:
CODE
NameVirtualHost 127.0.0.1
<VirtualHost 127.0.0.1>
DocumentRoot "C:\My Sites\Site1"
ServerName site1.local
</VirtualHost>
<VirtualHost 127.0.0.1>
DocumentRoot "C:\My Sites\Site2"
ServerName site2.local
</VirtualHost>
Okay, so this is the default. It is very customizable. Usually you say, "IP 192.168.1.100 goes to www.site1.com" But I think you can also do addresses. I've gotten this to work with dynamic dns where I couldn't rely on a static IP address.
I'm a little tired, so I can't give you the whole scoop. But just Google search for 'apache virtualhosts' and you will find some good information and tutorials.
Hope this helps.