hi,
are you using a name-based virtual host or an ip-based host?
basically, name-based means hosting multiple websites from one ip address
here is an example extract from the apache documentation page :
NameVirtualHost *
<VirtualHost *>
ServerName www.domain.tld
ServerAlias domain.tld *.domain.tld
DocumentRoot /www/domain
</VirtualHost>
<VirtualHost *>
ServerName www.otherdomain.tld
DocumentRoot /www/otherdomain
</VirtualHost>
try coping the above into your configuration file, and altering it to your needs
if all else fails, this:
http://httpd.apache.org/docs-2.0/vhosts/ will be quite useful