Ok, I'm not sure I'm understanding you, so if what I say next is off the mark, that's why.
The Android Market and App Store are completely separate, and the apps are not interchangeable. It's like trying to run a Windows app on a Mac. Not going to work. (Well, unless you running Windows on a Mac)
You can't re-dowload an app that you bought from the Market using your Google credentials. You'll have to use your Apple ID and pay, yes again, for the app.
Scroll down to the bottom of the App Store screen while in the Featured tab. At the bottom left make sure you are signed in with your Apple ID.
