1. Registering vbscript.dll
regsvr32 "C:\windows\system32\vbscript.dll"
2. Installing Microsoft Core XML Services (MSXML) 4.0 SP2 In Windows Vista Compatibility Mode
3. Running ArcGIS 9.3 Installation With Elevated Permissions
REF:
Installing ArcGIS 9.3 On Microsoft Windows 7
ADDITIONAL:
Installing ArcGIS 9.3.1 And ArcGIS Server 9.3.1 On Microsoft Windows 7