A Domain Shared by multiple web server

I do not know how to put this.
Maybe an example might help.

I have a domain, website e.g. www.abc.com
which reside on the server of my ISP.

Now I want the website to link to my subweb on my server while maintaining the same domain.

e.g. http://download.abc.com

The user traffic will be direct to my server.
How do I do this?

Reason: I will want to host my own website. but I still have two years contract with the ISP. Hosting by myself will definitely give me much flexibility.