Hey, welcome on the win2k8workstation forums! If you have a German Vista installation it’s very easy to just copy all de-DE (or whatever they call it) folders to your Windows 2008 pc. If you don’t have an other (suitable) pc and doesn’t want to have a dual-boot you can easily install a virtualization application like Hyper-V (only included in win2k8 x64), Microsoft Virtual PC 2007 or one of the many non-Microsoft applications.
See you around! 😉