I'm really struggling to get my head around how to do this - in part, I'm really a blank slate when it comes to the whole DNS stuff.
We have our new website set up on DreamHost. We now want domain requests (mail and web) for our existing domain (registered with MelbourneIT) to go to DreamHost i.e. web requests to the new website and mail to keep using our existing mail provider.
Can someone explain what I need to do conceptually (and simply) what I need to do with the settings at MelbourneIT and then also within DreamHost?
 I think I understand the MelbourneIT side - I just change the name servers (i.e. redelegate the domain name).
I just need advice on how to tell dreamhost how to handle requests to the domain name.
Am I getting there?