Some advice...

I can't provide any help in recommending which OS version to use, but you can currently get any of them from HardCoreMac .

 

You can run any OS up to 9.1, however any version of 9 will run terribly on that machine, at least that's what I found.

Depending on how much RAM you have, I would look into 8.6 as a compromise of features/usability.

Also, 7.5 has been public domained by Apple, so you can d/l and reinstall 7.5 for free:
ftp://ftp.apple.com/Apple_Support_A.../System/Older_System/System_7.5_Version_7.5.3

 

I work with older macs often. Ummm... Mac OS 8 would be the best bet. You should upgrade the memory (RAM) and you should either upgrade teh Hard Drive, or ad an external one, Mac OS 8 takes up around 100mb with some extras, so at least a 500mb external HD would give your Mac 6100 some room to breathe. go to crucial.com for memory, just use the easy pulldown menu. Your Power Macintosh 6100 is a PowerPC right?

Hope I have helped

 

Also if you want another mac for your class go to Mac of All Trades, www.macofalltrades.com they have very afordable Older Macs (under teh Older Macs section) Most of them are less than $50 dollars. Well I knew as a kid I loved the Macs in school, but I guess thats because I'm a Mac Head, lol Well Macs are great for education. There is a ton of software for kids and schools. If you need any help with older Macs just Private Message or E-Mail me

Also @ Mac of all Trades they have a Mac 6100, like yours, with 1 Gigabyte of hard drive space and 128mb of RAM, its only $19.99! Go check it out got to www.macofalltrades.com and clcik on Older Macs, I have shoped there before and they have great service, also check out the Peripherals to see if they have anything you like. Talk to you later

 

Hi
I also work in education, and we still use 5400's (and 575's)in our district. What we use on them is either 7.6.1, because it allows DHCP, and in one lab we use 8.6. In either case the machines run slow, but they still work.
If you don't want to do any upgrades to the machine other than OS, go with 7.6.1. If you want to upgrade HW, go with 8.

My .02

 

Well, my Performa 5200 (75 Mhz) is working slow-but-fine under OS 9, though it takes more than 5 minutes to start. Adding more RAM and a Hard Drive really helps.
And if you are going to buy some more old Macs, go straight for Performa! TV tuner and ability (with the internal modem) to answer the phone via the built-in mic, rem. control etc...

And the Monitor still works, though not like the new one.

 

I installed 8.6 on a 1994 vintage PowerBook 520c, and it actually works great. If I recall, there were some major networking improvements in the last few versions of 8.6 that might help you with your Ethernet problems (the control panel totally changed, I remember). On the PowerBook 520c I could run Interner Explorer 5, and with a broadband ethernet connection it actually browsed the web about as fast as a new machine using a 56K modem.