I have a domain name, say acme.com. I would like to be able to use an extended domain, say bluebeard.acme.com

Can I set this up without having to register a new domain name or setting up a new hosting site?

That would just be a subdomain. Does you host offer them as part of your package?

Once you are there, this should help;

http://content.websitegear.com/article/subdomain_setup.htm

At home I have a small LAN with www (web server), mother (desktop) and pvr (Personal video recorder). Internally, pvr.mydomain.com takes me to the PVR, but I think on the web you need to edit your DNS settings. As SJ says, I think this is down to your hosts. I am with one and one and you can choose to use their DNS settings or do your own. Setting up your own DNS server is not for the faint hearted! Is it a rented server or your own?

Thanks for the info.

I'm not sure if it's easier or more difficult than I thought!

My domain is hosted by Iomart, so I'll try and get an answer from them.

More thanks. Subdomain set up and working!

Excellent neileg, glad you got it sorted.