Can I set up windows update to use the second drive for future updates?

"Hopefully I don't get a -1 for this as it doesn't pertain to the uninstall folders directly. But will help with this users space issue and the moving of the update files.

You could move some of the other folders since it seems the uninstall folders are hard coded? A good one would be C:\Windows\SoftwareDistribution folder (where updates, etc. are downloaded to), however Microsoft says you can't move this one either, but you can if you use the Microsoft (Sysinternals) Junction tool (I always extract it to the root of my C:\Windows folder as it is used from the command prompt). This tool in essence redirects data from one location to another, the computer thinks the folder still exists in its original location even though you moved it. I use it all the time for this folder and others like the i386 folder instead of changing the registry.

Adding a Junction

First you will need to stop the Windows Update Service and copy the SoftwareDistribution folder to your other drive (with permissions). Start a Command Promt (cmd) via Start > Run > cmd, then :

net stop wuauserv
xcopy C:\Windows\SoftwareDistribution D:\Windows\SoftwareDistribution /O /X /E /H /K

Windows will ask you if D:\Windows\SoftwareDistribution specifies a file name or directory name (F = file, D = directory)?

Answer D for directory

Second you will rename the old folder.

rename C:\Windows\SoftwareDistribution SoftwareDistribution.del

Third step is to create the Junction (also from the command prompt) :

junction C:\Windows\SoftwareDistribution ""D:\Windows\SoftwareDistribution""

Forth is to restart the Windows Update Service :

net start wuauserv

See if you can download an update. If it works, delete the SoftwareDistribution.del folder, if not, try again or rename the SoftwareDistribution.del file back.

Remove the Junction

To delete the Junction if for some reason you don't want it anymore. Stop the Windows Update Service and copy the Software Distribution files back to the Windows folder :

net stop wuauserv
xcopy D:\Windows\SoftwareDistribution C:\Windows\SoftwareDistribution /O /X /E /H /K

Next delete the juction with -d :

junction -d D:\Windows\SoftwareDistribution

Then restart the Windows Update Service :

net start wuauserv

See what folders have a Junction :

junction -s c:\"

I think you're approaching this from the wrong end, I'd recommend making the C drive bigger. If it's a partition try using the gparted live CD from http://gparted.sourceforge.net/ to resize your partitions. If it's a hard drive I'd replace it. Sorry it's not a direct answer to your question.