Windows Vista and Windows 7 require the High-DPI-Aware has to be declared in the exe file manifest othervise the user interface runs in 96 DPI independently on the user DPI settings. For more information see http://msdn.microsoft.com/en-us/library/ee417691\(VS.85).aspx#_1.8
NSIS now has a ManifestDPIAware attribute you can set...