When you install a different anti-virus software such as mcaffee or Norton, do you have to delete on

Is it true that you can't install two antivirus software while the other one is still installed in the computer. Is this also true with Firewall?

When you install a different anti-virus software such as mcaffee or Norton, do you have to delete one first ?virus scan

ALWAYS, ALWAYS, ALWAYS with regards to the AV. Always delete first before installing second. If you know how, cull Program Files and Registry of old stuff too.

Windows XP and Vista may only run one firewall at a time but having multiple firewalls will probably cause your computer to really slow down and may cause crashes due to conflicts between the firewalls.

When you install a different anti-virus software such as mcaffee or Norton, do you have to delete one first ?anti virus scan

Delete one of them because they will conflict with each outher

and please say away from Noron.
You can install two anti virus however you can only run one in real time. You cannot run both in real time as they would conflict each other. But it is better to have just one antivirus though.
YES THIS IS TRUE YOU CAN'T HAVE TO TYPES OF ANTI-VIRUS SYSTEMS IN YOUR COMPUTER AT ONE TIME I HAVE NORTON AND IT RUNS GREAT YES IF YOU HAVE MC AFEE DELETE IT THEN INSTALL NORTONS YOU'LL BE ALOT BETTER OFF...... GOOD LUCK
u don't have to actually delete one of them but u do have to disable it