Depends on the software. Most modern packages allow for this type of installation via the ALLUSERS=1 MSI property. If you have an older legacy application that must be installed for every user (doubtful) then if you are an AD shop I would use a required once policy for all the ldap users.
You could always use the Active Setup feature of Windows to accomplish this. If you're not sure how Active Setup works, see: http://www.etlengineering.com/installer/activesetup.txt for a good explanation.
You would then package up your Active Setup reg keys and use LANDesk to install that on the PCs. When a user logs in Active Setup would start up the install as per your setup. The nice part of this is that it will fire once only for all exisiting or new users.
Active Setup works like a champ! Thanks!