When running FO fullscreen on WinXP, while using a firewall such as ZoneAlarm, when FO attempts to communicate with the server using networking, the firewall interprets this as internet access, and pops up a dialog requiring user approval. This dialog completely halts FO's execution until it is dismissed. This is fine for the server or AI programs, as the FO program itself can be minimized to deal with the dialogs.
But when the FO client tries to use networking when in fullscreen mode, the firewall program halts FO while it has fullscreen focus, effectively freezing the machine. There's no way to alt-tab or ctl-alt-del to close FO, as none of the windows GUI or Zonealarm popups can steal focus from or render over top of the hung FO program.
Windows and other programs seem to be still running, as moving the mouse cursor around causes it to change from windows white-with-black-outline, to FO black-with-white-outline, presumably depending on whether the cursor is over the task manager or ZoneAlarm popup, even though these windows can't be seen over the FO window.
In order to remedy this, I suggest having FO attempt to do something using local or internet networking that triggers ZoneAlarm or similar program's net-access verifier immediately when launched, before taking fullscreen focus. This way, the popup will halt FO, but in a state where FO is not in fullscreen mode and thus without preventing the popup from being displayed.
Yes, this is arguably a flaw with windows and ZoneAlarm, but it also renders FO unplayable and completely hangs a machine when it occurs, so should probably be dealt with.
An additional or alternative fix would be to have a popup dialog in FO when networking is about to be used for the first time (separately for local and actual internet), that requests that the user ensure that their firewall is set to allow FO to use networking, local or internet. This would be displayed only once (or twice: once for local, once for internet), and probably only on windows machines, as I assume there are no similar issues on linux or other OS's.
Putting a note about ZoneAlarm in the release notes is not really a solution, as people won't read these before trying out the program, and will thus just have FO apparently hang their machine when run.
(I assume that there's no way to make FO not apparently hang the machine while it is halted by ZoneAlarm while it has fullscreen focus, despite other progarms in fullscreen mode allowing the zonealarm popup to appear over them in similar situations)