I have a dedicated server which has a couple of IP Addresses assigned to it which have all been used up. I would like to add a domain pointer to one of my sites and was wondering if I need to put this domain name in the DNS? If this is required then I'll need to spend $15 for 15 more IP addresses so I'm hoping there's some way to do this without having to put it in DNS.

Also, how can I point the domain name to a subfolder off of one of my other sites and keep the other domain in the URL the whole time?

My server is running Apache with Red Hat.