Locating an Application to Launch

[David Burgun]

Hi,

How can I find out if an Application is available on the system, 
especially if there is more than one version of the application 
installed? I need something that will search all volumes on a system 
and list all the occurances of the application?

For instance if I am looking for (say) Photoshop and there are three 
versions on two volumes, I would like to present this to the user and 
allow them to select the one they wish to launch. If there is only 
one version, then just launch it.

This needs to run under MacOS X and Windows.

Thanks a lot for your help
All the Best
Dave