Does anyone know if Garageband software is compatible with the iMac ( flat panel) ?

Apple called the iMac "Flat Panel" only in terms of the iMac G4. The one with a white dome and a display on an arm above it. 10.6 will not run on an iMac "Flat Panel". And you posted this question to the 10.7 forum. The bigger question is, which iMac do you really have? And which one do you want to run Garageband on? And what version of Garageband are you asking if it is compatible? See this tip with references to iLife system requirements to help you find the answers you are looking for:

https://discussions.apple.com/docs/DOC-1707

And this one to determine if you have 10.6 or 10.7 compatible iMac:

https://discussions.apple.com/docs/DOC-2455

10.6 is the operating system known as Snow Leopard. 10.7 is the operating system known as Lion. You referenced

>HT3258: Mac OS X v10.6, OS X Lion: About incompatible software

As the subject of this thread which made no sense when discussing a Flat Panel iMac.

You might as well have asked can I run leaded gas on a Saturn. All Saturn cars were manufactured after cars went to unleaded gas, so the question makes no sense.

There *is* a compatible version of GarageBand for your computer, but we need to know exactly which computer you have to help you.

From the Apple menu at the upper left select "About this mac" and tell us what it says.