I have a web site on which I wish to enable instant messaging via IRC. Now I am about to buy VPS to host the ircd on. So, I will have two servers: one is for the web site and the other is for the ircd. The question is how to use the web site's domain name for the ircd?
With a subdomain such that example.com and www.example.com resolves the ip address of your webhosting server and irc.example.com resolves to the ip address of your irc server. People can then connect to irc.example.com from their irc client.
Also, do double check running an irc server is ok with your vps provider. Quite a few of them don't allow irc servers.