Форуми / Cotonti / Support / mod_rewrite Question

I am a noob with this subject... so here's my noobish question:

Situation:
I have a subdomain: subdomain.Mydomain.com
And I have registred an domain name lets say: domainname.com

On My subdomain I install a cotonti
And I let the domainname.com point to that subdomain.... (dns)

Can I rewrite the subdomain.Mydomain.com to domainname.com

So that it looks like you are on domainname.com (all the time) while in fact you are on a subdomain of another domain.

I hope this is explained correctly... Question is.. Is this possible