I'm not sure what you mean by "where they are stored." Your apps are stored in your downloads section in the Market. Where are they stored on the phone exactly? That I don't know. Some of us who are rooted have them in our SD card but most people have them stored in the devices memory.
I'm not talking about the program after its installed. I'm talking about the physical file you download from the market before it gets installed. Is there a location where the apk or executable equivalent is stored on the phone?
I have an app on my phone that is no longer in the market that I like and use. When I update roms on my rooted droid. Its not there and I Can't download it. Its not in the market anymore for whatever reason. I have to restore my backup to use it. I would like to get the installer file for it so I can put it on my updated rom.
Flash back to the rom that the app you would like to have is on, buy Root Explorer from the market open it and go into Data and long press the "app" file and copy it and place it on the root of your SD, I do the same thing with the Data/App and System/App file when switching Roms this way I have access to my previous Data and System/apps
Flash foward to your new Rom open Root Explorer find the Data/App file you pasted on the root of your Sd, find the app you would like to install, short press it and select "install"
In the Data/App file, you need Root Access and Explorer to be able to see those files.
I got so tired of the names falling off the edge of the widget when I rebooted the phone.
It worked the the picture on the widget changed too.