Yes it's possible to access the server before the domain is transferred.
This is the way if you have Windows 2000 or XP
You know the name of your server.
Ping it: Start / Run. Write cmd
The command prompt open.
Write ping YouServerName (ex: ping franc.dreamhost.com)
You will see is IP address. Note it.
Open the hosts file of your computer (it should be in: Windows\System32\drivers\etc) if not, do a search
Open this file with Notepad.
Add the value of your server as explained in the host file.
ip address [tab] domainname
ex: 126.96.36.199 domainname.com
Save the file.
Every time you will enter your domainname in a browser, it will point on your new server. So you can upload and setup everything before changing DNS of your domain.
if you run an older version of Windows, the "cmd" is replaced by "command" and the host file is not in the same place. But overal, it'S the same step.