Downgrading Fees

Hello,
I am trying to install W2003 Server. I am told that MS no longer do 2003 Server licences, and that now the only way of getting a licensed W2003 Server installation is to use 2008 server media. I've been given a legitimate licensed 2008 Server DVD, apparently downloaded from MS. However, when I run it I see no option to install 2003 Server, and after I've run through the installation of 2008 Server, I do not see any way
- to downgrade the 2008 Server installation to 2003 Server
- to create a 2003 licence key from the 2008 licence key for use with 2003 Server media.

I also want to know if I hav eto pay Extra Fees for downgrading