The following might help as well!
Error, "The Temp folder is on a drive that is full..." when installing
Acrobat 8 trial or Adobe Reader 8 (Windows Vista)
Issue
When you install Adobe Reader 8 on Windows Vista you see the error message,
"The Temp folder is on a drive that is full or is inaccessible. Free up space
on the drive or verify that you have write permission on the Temp folder."
Reason
You have turned off User Account Control or you are logged in using the
default administrator account.
Solution
Do one of the following solutions:
Solution 1: Enable User Account Control.
In Control Panels, choose User Accounts.
Click "Turn User Account Control on or off".
Check the box to "Use User Account Control (UAC) to help protect your
computer" and then click OK.
Restart your computer.
Install Adobe Reader 8.
Note: You can turn off User Account Control after you successfully install
Adobe Reader.
Solution 2: Run the installer in XP Compatibility Mode.
Download the Adobe Reader installer from the Adobe website. When you are
prompted to run or save the file, choose save. Save the file to your desktop.
On the Desktop, right-click the AdbeRdr80_en_US file and then choose
Properties.
Click the Compatibility tab.
Under Compatibility Mode, check Run this program in compatibility mode for:
and choose Windows XP (Service Pack 2) from the drop down list.
Click Apply, then click OK to close the Properties window
Double-click the AdbeRdr80_en_US file and continue with the installation.