R2008a happens to be the first release that used the newer license scheme. If you had been asking about r2007b or earlier, you would probably have needed to get Mathworks support to assist you to create a PLP for you.
But with R2008a and later you might be able to process this yourself.
What you need is to find a valid Professional / Standard / business license for R2008a or later that can be activated for the target system. Using that license you would be able to download and install any release from the last one you paid for on that license or earlier right back to MATLAB 6 or so.
This is not something that could done with a Student licence or Home license.
You are potentially using an Academic license. The terms of the Academic licenses seem to vary. I have seen credible claims that some universities are only authorized for one particular release, but I have seen more reasons to suspect that those might be reluctance from university staff rather than actual contract limitations.
If I recall correctly, in Germany you are probably covered by an Total Academic Headcount (TAH) licence and that there is no contract restriction against your installing older releases just by downloading the installer and activating against your current TAH license. So I suspect that you can do this without needing Mathworks to get involved.
