Hi hsn22, as David suggested, the migration guide includes relevant info about this.
Beside, probably you are referring to the fact that when you open a sample project in Eclipse, it tries to use Android 4.x by default (and the AndroidManifest also uses elements that are available only in ICS, such as the "screenSize" and "smallestScreenSize" attributes);
in this case you have two options:
1. install Android 4.0 or 4.1 using the SDK manager in Eclipse (then the project will compile, but you will still be able to deploy and run it on a 2.2 device, because the min-sdk version of the project is still set to 8, despite the fact that the target-sdk is set to 14 or 16);
2. change the project settings to use Android 2.2 (or a version of your choice); in this case, though, you will need to manually remove the "screenSize" and "smallestScreenSize" attributes from the AndroidManifest, as they will be highlighted in red by Eclipse.
Option 1 is preferrable.
I hope this helps.