Detect installed application

I have a startup script that installs an application. What i want to do initially is detect if the application is installed and the version number; at this point it either carries on with the install or closes out depending on the information retreived.

That is if it is installed and is version 1.0.1 then end the script; if it is installed and is version 1.0.0, install; or if it isn't installed at all then install.

Make sense?

I'm not stuck on batch scripts but I am deploying through GPO so am a bit limited i think.

Anyone help?

emr