that would be an Apache configuration issue
you would have to create separate 'virtual hosts' in Apache for each domain, and set the 'document root' of each virtual host to the appropriate directory
you can download and install webmin
http://webmin.com/ if you need a gui to help you with it
if not you can look at this doccumentation on how to manually configure virtual hosts
http://httpd.apache.org/docs/1.3/vhosts/