This update is only meant for certain Macs. Please read the read me text available at Apple's FTP Sites.
System 7.5.5 Update
This was released in September.
Apple is delivering its final system software release for the Macintosh Plus, SE, Classic, Portable, PowerBook 100, SE FDHD, SE/30, LC, II, IIx, and IIcx. These computers were not designed to support 32-bit memory addressing. Future Mac OS releases will require 32-bit memory addressing, which is supported by all other Macintosh models.
System 7.6 
(Needs to be purchased)
PowerPC Interupt Extension(Note 7)
 
Open Transport 1.1.2
 
Open Transport/PPP 1.0
 
Apple Laserwriter Driver
 
Laserwriter 7.2 (Note 3)
Laserwriter 8.2f (Note 4)
LaserWriter 8.4.1 (Note 8)
Notes:
1. This will change the version number to 7.0ΓÇó
2. This will change the version number to 7.5.1
3. It may be recommended that both versions of the Laserwriter software be installed. Some programs do not work with version 8.2.2 and 8.3 and you may print faster with version 7.2.
4. This version of the Laserwriter software is meant for those users that own Apple printers with internal FAX boards.
5. This update will update all Macintosh computers to System 7.5.3 and will also install Open Transport 1.1.
6. This updater corrects problems with the Apple Vision Displays after installation of the 7.5.3 update.
7. Should be installed on all PowerPC's that are running System 7.5.5.
8. This should not be installed on non-PowerPC Macs unless you have the CFM-68K Fix from Apple.
This is not meant to be a list by which everyone should configure their computers. It is only meant to be a quick reference list of the latest versions of major software releases from Apple and which computers they should be used on.