Transitioning 2003 domain to 2008

Hello,

I have a problem with migrating my Windows 2003R2 domaincontroller to a 2008R2 domain controller.
I have on the moment a 2003R2 x32 server running, this is the only domainserver in my small network. This server is now about 5 years old and I want to replace it with a new 2008R2 x64 server, this server must gonna act as the new domain controller. The old 2003 server must be demoted an gonna act as file/application server.
On the internet I found some good tutorials over transitioning your domain from 2003 to 2008 which can be followed to complete this task.

Still the following problem occure.
When I'm on my 2003 server run the command,  adprep / forestprep, I get the message that everything is already up to date and as a consequence that no action is been taken. (Maybe things already here gone wrong?)
I made my new installed 2008 server member of the domain, after that I run the dcpromo command, I choose for the option extra domaincontroller in existing forest. I get the error, that I must run the adprep /forestprep command to prepare the forest. The adprep can be found on the dvd of the 2008R2.

What I'am doing wrong? Hope someone has a tip for me.

Thanks.