Hello, Joe Fisher, a new 2400 user here again - Which OS gives the 2400 the best speed & performance? (ie when does the OS upgrade factor begin showing the limits of even a fully upgraded machine or what OS upgrades result in the need for Houdini style tactics to load on a 2400 etc.) The 2400 I recently purchased has 8.1 loaded on it. I own CDs for 8.5 & 9.2.2 (as well as OS X all vers. but I don't want to load OS X) I've read 9.1 is the highest OS that can be loaded. Currently it's selling for about $19-25 on e-bay I have plenty of "Classic" software which will do me fine - As mentioned in prior posting - This machine will eventually get a 240MHz daughter card & the 80 MB RAM treatment. BUT I want it to remain quick and nimble as a commuting machine for travel as well as home/office commute.