Hi,
I would recommend you to disable messenger service on windows XP.I guess your OS is windows XP SP1.You should strongly consider updating to SP3
http://support.microsoft.com/kb/330904
Also use this symantec tool to restore access to regedit/task manager
http://securityresponse.symantec.com/avcenter/UnHookExec.inf
Just save UnHookExec.inf and install it by right clicking and selecting install. Installing the file will not show any popup or notice box.