Do yuo want to deploy it silent in your organization, then i think you need to get the MSI installer by following this link http://www.adobe.com/products/reader/distribution.html
else if you are just installing it in your computer why dont you follow the http://get.adobe.com/reader/
Command Line Switches for the Bootstrap Web Installer for Reader are provided below:
/sAll Silent Mode for product
/sPB Silent Mode with Progress Bar for product
/rs Reboot Suppress
/rps Reboot Prompt Suppress
/ini "PATH" Alternative initialization file
/sl "LANG_ID" Set Language; LANG_ID - Code in decimal digits
/l Enable Error Logging. Log file Bootstrap.log will be generated in temp directory
/msi[Command line] Parameters for MSIEXEC
AdobeReaderInstallFile.exe /sAll /rs /l /msi "/qb-! /norestart ALLUSERS=1 EULA_ACCEPT=YES SUPPRESS_APP_LAUNCH=YES"
This command line has parameters for both silent install (/sAll) as well as progress bar mode (/qb) which is useless. Also /rs and /norestart work the same way supressing the reboot.
SUPPRESS_APP_LAUNCH=YES can also be removed as the checkbox for suppressing the application launch after install has been removed from the installer.
Moreover the quotes are not being recognised by the MSI Installer causing it to launch help window pop up.
So the command that can be used for silent install and suppressing EULA is:
AdbeRdr_1000_en_US.exe /sAll /msi /norestart ALLUSERS=1 EULA_ACCEPT=YES
If you haven't resolved this issue yet, may I ask what operating system are you using? Are you able to install Adobe Reader 5.1 on on a different OS, attempt upgrading and replicate the issue?