I think this is the file you need. You will have to unarchive it prior to copying it to the system folder of your boot floppy:
http://download.info.apple.com/Apple_Support_Area/Apple_Software_Updates/English-North_American/Macintosh/System/Older_System/System_Enablers/System_Enabler_040_1.1.sea.bin

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I already have the System Enabler. There just doesn't seem to be a System Folder on the Install floppy. I copied the System Enabler to the root of the floppy disk and now it gives me either one of the following two messages:

Sad Mac with the codes:0000000F

00000066

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or

Not enough memory is available while using "System"
To temporarily turn off extensions, restart and hold down the shift key.

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Does anyone know how to fix these error messages?