Now .NET 3.5 is shipping I took the opportunity to update one of our internal applications and elected to have it install the necessary components (in this case the .NET Framework 3.5) using the
Download prerequisites from the same location as my application option.
When trying to install the application via the IIS web server the installer would fail with a download error.
A little testing later I realized the publishing mechanism had placed .msu and .msp files for prerequisites onto the server and of course IIS 6.0 does not serve unknown MIME types.
Both .msu and .msp extensions must be added into the MIME database as application/octet-stream via MMC.
And all was well again.