It would be nice if the Install Conditions for prerequisties were more flexible.
for example We require .NET 2.0 runtime, so in the "Search" stage we check if it is installed and we also check the source directory for the installer. If it isn't installed but the installer is present (as is the case if installing from the CD) then a custom action launches the installer before continuing. However if the installer is not present (downloaded from the website) then we would like the software prerequisite to fire enabling the user to automatically download the installer.
However the prerequisite is appears to be checked prior to the search and any of the custom actions.