network problem

I have a small home LAN that I am starting to upgrade from FC9 to FC10. As the network is still "hardwired" with ethernet cable and the boxes all have static IP addresses I would like to continue using the old network service rather than NetworkManager. After installing FC10 on one of the machines without problems, I stopped and disabled NetworkManager and configured the network using the widget System -> Administration -> Network from the gnome desktop and filling in the "DNS" and "Hosts" information as with FC9. But then I made a typo in editing device etho under the "Devices" tab -- I accidentally typed in the gateway address instead of 255.255.255.0 in the "Subnet mask" field. Now whenever I try correcting this from the "network" widget the field reverts back to what I mistakenly typed in before. This is apparently why I can't reach the network from this box. Is there an easy fix to this -- short of doing the installation over? Thanks for the help! Jerry