I was able to remove the Task Scheduler patch (KB841873) and get my Tasks to execute again, correctly.
There is a suitable workaround for the original security problem described on http://www.microsoft.com/technet/security/bulletin/ms04-022.mspx under "Vulnerability Details"->Workarounds for Task Scheduler Vulnerability".
If you have SP2 installed, I assume uninstalling SP2 would also allow it to be fixed. I don't have SP2 installed, as when I did install it, too many different things all failed at once. I went through all the proper "procedures", making sure there were no programs running that might interfere, but after installation, previous programs I depend on refused to run or wouldn't work over the internet (I disabled the SP2 firewall as I already have that covered with a 3rd party, two way firewall).
I find it amusing that Microsoft claims Longhorn is faster than Windows XP -- so it was faster over Win98, but both Service Packs slowed down WinXP. In some cases the slowdown was "permanent" -- no workaround to be provided. Indeed MS security updates broke my Outlook-2002 working with the IMAP protocol. I wasn't able to roll those back as my saved system states were corrupted after installing the MS Critical Security fixes. I did analyze the IMAP traffic generated by Outlook -- and when it would hang/ hangs (doesn't always hang, some timing problem), Outlook doesn't send the IMAP equivalent of "end of commands, now run". The result is the IMAP server waits (I think it waits about 20-30 minutes), and the Outlook client is "waiting" for a response from the server that never comes. About 50% of the time, trying to cancel the operation in Outlook will result in Outlook hanging (program not responding) and having to be killed from the Task Manager.
In short -- back out the broken MS patches and wait till MS has a patch to correct the problem(s) introduced by the "critical patches".