Arjan,
We’ve had a few folks report issues on Win2k3, while I’ve personally tested on both Win2k3 and Windows XP Pro 64-bit which is based on the 2k3 platform, both have worked for me… but that is hardly helpful for you I know.
In the cases where the installer gets pissy, we always suggest people use the Manual Install, which I imagine as a long time user you have probably used by now. I’ll make a note in our issue tracker to get a 2k3 machine setup to re-test on though, the InstallShield installer can get squirrely.