How can I stop Windows from blocking McAfee Antivirus updates?

Perhaps you could reinstall the Antivirus?  Then you could try to do the update.  What is the error message that you get when you say it gets "blocked"?

When I attempt to install the latest superdat file it indicates that the file is not signed or is unknown then it fails with an error message that says "windows has encounted an error or issue with file"

Sounds like you've got an infection.  Check your hosts file, although I don't think this is the problem it can't hurt, windows->system32->drivers->etc->hosts

You should have one uncommented line there

127.0.0.1       localhost

If everything is okay there (if not delete all other lines), you next to to run Malwarebytes.  download it from here:

http://majorgeeks.com/download.php?det=5756

IMPORTANT: rename the file before it downloads to mb.exe.

Next run mb.exe.  If you can't run it post back here.

If it is a malware, you could also use the following:

http://www.combofix.org/

Download ComboFix.exe to c:\ drive

Log in to Safe Mode and run Combofix.exe.  It should clean up your pc of most malware

Ztucker, I've done the checks you recommeded except malware check. Instead, I've installed McAfee Virus Scan 8 on multiple clean laptops, however, when I attempt to install the superdat I get the error message attached. This is the same error message that I got when this issue first manifested itself. I'm covinced that this is not a malware issue because I was to install and update McAfee Virus scan 2010. I suspect that the reall issue here is that McAfee might have stopped supporting Virus scan 8 therehore none of their DATS or Superdats will not work with it.

Sorry, attached is the error message I mentioned above.
McAfeeAVError.bmp

I'm surprised you want to stay with McAfee after the recent debacle.  That recent update they pushed out (5758?) hobbled more machines then I care to guess.  You may wish to Change rather than upgrade.