Inno - How to only install if file already exists

I use Inno for my applications deployment. No problem with that.

But I also use Inno to deploy upgrades and updates so what I'd like is for Inno to check if a file already exists on the user's computer and if it doesn't then the installation (upgrade) should abort and display a message to the user.

I guess I need to use some script for that ?

Anyone point me in the right direction ?

Thanks
Ian

i had a look at this site for downloading.......

should i go for the stable release download or the Quick start pack?

i am using vs 2005