it, turn it off, and maybe uninstall. If these are PoS boxen, do you need X windows? Do you need Gnome or KDE as windonw managers (look at smaller ones - I use IceWM at home, < 600k, yes, k, not M; the other admin here likes xfce)?
I have the CentOS Extras XFCE on one of them (for which I could actually get the right additional RAM), but most just run headless (and were installed with the text installer).
I don't use them as cashier machines, just got them second hand. They were so cheap that I bought one just to try, and then found it so good that I bought the other three... (I'm probably not the only one on this list who has computers all over the place, and a wife who gave up asking when you come up with a "new" one)