I think there's some performance issues with the NSIS System plugin and Windows Vista.
I really need Vista testers for this, but some XP machines are needed also as a baseline.
If you would like to help my testing, please download the zip file, and run each EXE. It should popup a dialog box in 10-20 seconds. During this time, could you open Task Manager and watch the CPU usage for the executable. Please report back the EXE you ran, the average CPU usage, and the time elapsed (from the dialog).
And would the Vista testers also say whether or not you have UAC on or off.