1. You cannot run System 7.5.2 on your PowerBook. System 7.5.2 was designed only for PCI based Power Macs. This is a Good Thing, too, as there's no real reason you'd want to run it. It was quite buggy, from what i've heard.2. Although you can copy the system foler you are currently using, it may not always work, as the System is always using files in the System folder, and those files won't copy. If you want to copy the system folder, then boot off the RamDisk you were talking about.
3. You need the Finder file. This file, as the name suggests, is the application file for the Finder application, which is your Mac's user interface. Without Finder, your computer will not start completly.
4. Yes, you can get internet access on your PowerBook. You can do it either by:
a) plugging your 56k modem directly into the PowerBook, and after setting up internet access, launching the internet applicaion of your choice (Netscape 4 and iCab are good browswers on LC '040s, and Claris Emailer and Outlook Express 4 are good email apps).
b) Using an internal modem you may already have instead of your external
c) Putting an internet sharing app onto the Quadra, to share your 56k modem with the rest of your network. I've heard that Vicom Internet Router is a good app.
Either way, good luck, and i hope this helps. 
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Give your dreams a chance.™ - Apple in the mid '90s
Warrior maclover5
68k Macintosh Liberation Army
Number of 68ks Liberated: 6
Performa/networking & 1 or 2 other things!(takes a
Posted - 10 Oct 2002 : 12:32:26
68k of the Week: kastegir's PowerBook 180.