First be sure to read this recent blog post that gives an overview of how applications see different screen sizes and can adjust to them:
http://android-developers.blogspot.com/2011/07/new-tools-for-managing-screen-sizes.html
This post has some examples of basic adjustments -- providing different layout files for different screen sizes.
This is also something that the fragment APIs are intended to help with. If you are already writing your UI with fragments, you are most of the way there -- showing these in tabs does not require a totally different implementation, just use the fragments to populate the different tabs.
If you are targeting Android 3.0 or later, this is easy because the action bar already has simple mechanisms to have its tabs allow switching between fragments. This API demo provides a very simple example of its use:
http://developer.android.com/resources/samples/ApiDemos/src/com/example/android/apis/app/ActionBarTabs.html
If you want to run on older versions of the platform, that is what the fragment APIs in the v4 support library are for. These allow you to write your app using fragments and still be able to run all the way down to Android 1.6 (API 4) of the platform. In MR2 we also added some sample code showing how you can use the support lib fragments with the old tab API.
Sample code for this is included in the now deprecated TabActivity class:
http://developer.android.com/reference/android/app/TabActivity.html