Note: This is only recommended for CRT iMac users who cannot update using the 4.1.9 firmware.
There have only been two cases I know of where the 4.1.7 would update when the 4.1.9 would not.

The slot-load  (350 - 700 Mhz) iMac firmware update 4.1.7  had a short life, being replaced within 6 months
of its release by the 4.1.9 firmware update.  The 4.1.7 is not a recommended firmware update, nor is it available
from Apple Downloads. It will not update firmware with a build date later than March 20, 2001 --- (the 4.1.9 iMac
firmware has build date of September 14, 2001).

The 4.1.7 iMac firmware was  released on many new iMacs and was also available as a public download, at
one time, from Apple Downloads.  It was also considered a little buggy by most users but was a step above
older firmware. OS 9.1 or later must be installed before you run the 4.1.7 firmware update.

If you wish to install the 4.1.7 iMac firmware -- download the disk image here --->  4.1.7 firmware update 1.4 MB download
Read The Instructions Carefully before you begin the install.

If you successfully install the 4.1.7 firmware I highly recommend
updating to the 4.1.9 version found at Apple Downloads ---> iMac Firmware Update 4.1.9