I'm making some assumptions here. Correct me if I'm wrong.
Even though you're brand new on Dreamhost, I'm assuming you have (or will) install MT on Dreamhost. (You may still have your "old" host and want to keep MT there, too. It all depends on how you want to do it.)
In my case, my MT software is installed on Dreamhost "once". From there, I have created several blogs. I have several blogs spread over several domains and some blogs over several directories within the installed software domain.
Where MT is installed:
writes to domain1/mtblog/
Blog #2 to domain2.net
Blog #3 is domain1.com/differentdirectory/
If your intention is like mine of only installing Movable Type itself once you'll Login to MT, "press Create New Blog" and follow instructions there...
To create a new directory (if you have a single domain and thats what you want), I use WS_FTP and login to my domain webspace. I then click on MkDir and type the new directory name.
When you post to your blog, you'll use the same way you post to blog #1, but select blog #2 as your "New Entry".
This will hopefully get you started. If not, describe exactly how you'd like it to work (multiple domains or not, multiple directories or not, PC or Mac program to upload, MT installed on Dreamhost or elsewhere, etc.) and I or someone else here will be more than happy to help.
If you like you could even give specific domain names and directories and I can give you "exact" type this here type of instructions.
Welcome to Dreamhost.