Hello
I have the same kind of problem of system hang when installing NIS 2009 as reported by other users. It's on a Toshiba Tecra S10 running Vista Business SP1, but ZoneAlarm is not installed (and has never been). Installation was over the trial version of NIS 2008, the installer uninstalled it, rebooted the computer and the system hangs during installation of NIS 2009 when "starting services" - 100% CPU (well 50%, it's a dual core...) and the only way to exit is to shut down. Only way to fully recover the system is to use the Removal Tool. The only other security software used is Windows Defender, the Windows Firewall was disabled.
I used the removal tool with all services except Microsoft disabled, rebooted and tried to install NIS 2009 with services still disabled, but with exactly the same result.
A couple of weeks ago I succesfully installed NIS 2009 on a Dell Dimension running Vista Ultimate SP1, this time over the retail version of NIS 2008. Windows Defender was used and Windows Firewall was disabled, and the installation ran without a glitch.
Thanks!
[Edit: removed second kudos button]