Unfortunately, Windows Installer itself requires SP6, so you have no choice but to install it. You can get it from Microsoft at
http://www.microsoft.com/ntserver/nts/downloads/recommended/SP6/allSP6.asp
Note:
Because of US Government regulations, Windows NT is available with standard (40-bit) encryption and the restricted high (128-bit) encryption. SP6 is available in both versions; however, you may only download the US English and French Canadian versions of the high encryption version of SP6. If you need other language support and you are running the high encryption version of NT, you must get SP6 from a Microsoft CD; you cannot download it.
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