How to downgrade an iOS app for iPod touch? Is it possible to downgrade an app from a newer version to an older version without having a copy of the older verion.

I guess this could also be rephrased to, 'is it possible to download an older version of an app from the AppStore after the new version has been released'
If you have Time machine enabled or you don't empty your trash very often you're in luck. You can go into Time machine and simply roll back to an older version of the app in Finder. Then if you uninstall and reinstall the app from iTunes you'll get the older version. Apps are stored by default in /Users/YOURUSERNAME/Music/iTunes/iTunes Media/Mobile Applications if I'm not mistaken. Just find the older version in your trash or hit Time machine once you get to that directory and roll right on back.