Don't know McAfee but for outhers, you can check the registry for the uninstallstring. It will hold the command to ininstall. FE, when I rooled out NAV 7.5, I had to uninstall LDVP first.
code:

;  - check if VP5 is installed
;
$vp5uninstall = "C:\Program Files\LANDesk\VP5\vpremove.exe"
$isvp5installed = ReadValue("HKEY_LOCAL_MACHINE\software\microsoft\windows\currentversion\uninstall\ldvp 5.0", "uninstallstring")
if $isvp5installed <> $vp5uninstall goto skipuninstall
endif
if @INWIN = 2
MessageBox("NOTICE!" + Chr(13) + "LANDesk Virus Protect must first be uninstalled." + Chr(13) + "System must REBOOT when complete!" + Chr(13) + "Choose Yes to uninstall and Yes to reboot" + Chr(13) + "on the two options that follow","Norton AntiVirus 7.5 Install",48,60)
RUN "C:\Program Files\LANDesk\VP5\vpremove.exe"
goto finish
endif
RUN "C:\Program Files\LANDesk\VP5\vpremove.exe"
sleep( 1 )
setfocus("Uninstall Message")
sendkeys({ENTER})
sleep( 15 )
setfocus("Uninstall Message")
sendkeys({ENTER})
endif
;

There are a lot of posts on this board related to NAV and McAfee. Check out post:
http://kixtart.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=2&t=001912

_________________________
Give a man a fish and he will be back for more. Slap him with a fish and he will go away forever.