It's worth noting that not all 575s have CD-ROM drives... but aside from that, I personally think finding a way to install 7.5.3 from floppies should be mandatory for all new recruits – it builds character ;-)

Do either of them have ethernet? If not, I'd make that priority number one... it will make your life a lot easier and the NICs for those are (generally) cheap and plentiful. The 575 is a better machine than the 580... I have a couple that still get used daily. If you feel like throwing a few bucks at it, you can get a quick and easy performance boost with a 32MB RAM module and a 7200RPM hard disk. Both are pretty affordable upgrades if you shop around.