Subdomain Setup

Little frustrated because i feel like i should have been able to figure this out.

I have a domain with Custom DNS support through DynDNS, its points to a homeserver and i am hosting 3 websites on it. I have no problem with two of them

www.mysite1.com

www.mysite2.com

i am trying to attach my third site to a subdomain of http://www.old.mysite1.com

Now I believe that appache is set up correctly but the DNS is not pointing it to my homeserver.

What do i have to enter into my DynDNS set up to make this happen?

I have entries of:

old.mysite1.com / 600 / ns / http://mysite1.com

www.old.mysite1.com / 600 / ns / http://mysite1.com

Do i have the wrong type of record, or am i missing the whole point?
I am hoping that i don't have to purchase an entirely new Custom DNS to point at a subdomain. I can put in a workaround with the actual server, but it will not be a separate website, ill have to include a link. Its a small problem, but i feel like i should be able to make this happen through DNS and i'm being stubborn.