Following on from my last answer to you, the below is similar to the answer I gave before, but the install script has an extra line (CACLS) to give all users of the computer read access to the newly copied directory. If I am reading your question right, they should only need read access. If they do need write access change the "Users:R" bit below to "Users:C" (the C means change or modify access).
I've also change the %LOCALCACHE% variable to point directly to the msi folder and changed the msiexec accordingly so double check the paths on your DS task.
I also need to add that this works for us on XP SP3 and I've not tested on Win 7.
i) Copy File To - copy the directory of the source installation to a folder on the local computer, C:\JobSource\Apps\App1
ii) Run Script - a simple batch script to install the app, e.g.
REM Install Script
Set LOCALCACHE=C:\JobSource\Apps\App1
CACLS "%LOCALCACHE%" /e /p Users:R
msiexec /i "%LOCALCACHE%\App1.msi" ALLUSERS=1 /norestart /qb-
EXIT %ERRORLEVEL%
Hope this helps,
Darren.