Karsten,
Have you considered Wine, at:
http://www.winehq.org
It's an open source software implementation of the
Windows API in Wine. You don't need a Windows license
You can install your Windows programs from the CD into
a "fake" C drive (symlinked to a Linux directory) and
run it with:
$ wine windows-program.exe
Tools such as regedit are available as well, for
tweaking the installation.
Ira