command.com file error message

System
========
OS: WinXP home

Problem (command.com corrupted? or virus?)
==================================
1) After finishing installing zonealert firewall program, system prompt to
restart to finalise setting
However, during rebooting, there is a dos environmental prompt error msg
:"error: command.com file may be missing , damaged or corrupted"
System hanged at the dos environmental screen and had to power down and
reboot again.
After that, no error message seen when booting up

2) Afraid that pc may be infected by virus, I installed norton antivirus
2004. Updated the virius definition file and tried to do a full system scan
However, Norton stops half way after scanning about 100 files. the first
directory scanned is the I386 folder
System status on the Norton Anitivirus screen showed: "Status: Urgent
Attention required"

Qn
=====
i) Am I required to correct the command.com error?
has the OS autocorrect the command.com file as it is no longer showing the
error message when booting up?
will uninstalling the zonealert program help?

ii) Is the PC infected by virus as Norton is unable to do a full system scan?
will uninstalling the zonealert program help as that is the last software
before the system shows the command.com error message