AVG firewall can't close "Server Busy - switch to/retry"
Just for those who may run into this issue...
Problem happened (winlogon.exe missing comdlg32.dll) after power loss during XP boot. Corrupted NTFS fixed with "chkdisk /R" in repair shell, however core DLLs were missing. Manually extracted comdlg32.dll using "expand comdlg32.dl_" from XP CD, which enabled boot.
Once back at the desktop, avg wouldn't open avgui.exe, giving a "Server Busy" popup which could not be closed (without end tasking the process).
Not being able to start windows firewall gave me the clue - there were still a bunch of lost DLLs from windows, which were preventing windows services from starting.
A quick google found me the SOLUTOIN: start->run->"cmd"->"sfc /scannow" (and chuck the XP disk in)
This replaced the missing DLLs and I could open avg again, even before the repair had finished.