If you need to reserve a port in Windows Server 2008, 2008 R2 or SBS 2001 (which is in fact a 2008 R2), it does not make any sense to modify the registry value
as indicated at in the Microsoft KB 812873, because Windows Server 2008 and 2008 R2 does not support this setting anymore.
You need to request a hotfix from this page KB 2665809, install it and then you can control your port ranges with the commands (from an administrative command prompt of course):
netsh int ipv4 show excludedportrange protocol=tcp
to display active reservations, and add with
netsh int ipv4 add excludedportrange protocol=tcp startport=8000 numberofports=1
The command is documented at the MS KB page where you can find the hotfix.