Windows Installer falling foul of DEP

Hi,
I have come across a problem I cannot fathom. About three weeks ago, I
installed Adobe Acrobat3D (V8) trial from the Adobe site, it installed
without problems. A week or so ago, I had reason to re-install Vista Ultimate
from scratch (formatted disk) and now when I try to install Acrobat, the
installation is aborted by DEP. I downloaded the installer again with the
same results. The program halted by DEP is Windows Installer. I know that DEP
will hat a system program if the program being installed trys to install into
protected memory but why did it work before and not now. Vista is fully up to
date BTW.

I have noticed this behaviour more and more, programs that would run without
problem are now falling foul of DEP where they didn't before.

Anyone any ideas on how I can get around this? DEP cannot be turned off for
system programs so am I stuffed here? Back to XP for me if so, Acrobat3D will
be one application I will definately need to run.

Regards, Jeff

An update....

Just for old times sake, today I decided to have one last go at installing
Acrobat3D. Blow me but if it didn't install perfectly! Now, nothing has
changed on my machine at all other than a couple of Vista updates so why has
it now started working after so many failures?

At one point in the installation, it advises me that it need a windows
installer process (ID9714) terminating before it can continue, I cannot find
this process in Taskmanager so the question is:- This must be a hidden
process as I can't see it in Taskmanager so how can I find it to terminate it?

Regards, Jeff