NUnit 2.5.0 installation problem

I was trying to install NUnit msi package on my computer but the installer told me this: "Please wait while installer finishes determining your disk space requirements.". It hanged forever so I finished intallation. I thought some other running program probably blocks intallation for some reason. I tried to kill some running processes (IE 7.0, Firefox, MS Outlook) and run the installer again with success. I am not sure what exactly happened but it helped at least in my case.