Update: You can now download Windows Server 2003 R2 here: microsoft.com.
Today I attempted to install Windows Server 2003 Administration Tools Pack (adminpak.msi) but the installer instantly quit with the message “Windows Server 2003 Administration Tools Pack can only be installed on Windows XP Professional with QFE Q329357 applied, or on Windows XP Professional Service Pack 1 or later, or on computers running Windows Server 2003 operating systems.”
When researching if R2 needed a different version, I came upon the page “Windows Server 2003 R2 Administration Tools Pack (x86).” Judging from the title, I’d assume this was the file I was looking for but these files are actually for other OSes that want to manage the new services which come with R2. The only place I have found the adminpak.msi for 2k3 R2 has been on the CD itself. You can find the file within your i386 folder on your R2 CD.