Are the programs avg, zonealarm, and the programs associated with the quicklaunch shortcuts been installed and their contents not on your computer?
Sounds as though your registry has been altered, perhaps by a reg cleaning program or maybe when you installed Nero it installed these components as well. Or you may have done something when you were frantically trying to get that DVD to work eg you did a restore point or "last known good".
P4 Intel + desktop
Uninstalled Benq software and Nero Exp.6 after removing dud dvd drive. Then replaced new Atapi dvd drive and installed Nero Exp.6.6. Found some quicklanch shortcuts have disappeared from task bar and same in msconfig>starup list. Among items missing are AVG and Zonealarm. What could be happening here?