From Patrick Tisseghem's blog:
What about these MOSS 2007 policies? One part of the presentations is a talk about the new policy framework and the records repository. Good stuff, especially if you are an organization that wants to support the full life cycle of documents and this in a very controlled environment. Policies can be defined at the level of the site collection and then hooked up with a document library or defined specifically for the library itself. It is very easy to try out yourself.
Take for example a policy that requires research documents in a document library to have a label 'Research Document – Internal Use Only'. You can enforce this with the following steps:
1. Create a document library (anywhere)
2. Navigate to the Document Library Settings page using the Settings menu on the toolbar.
3. Click on Information Management Policies
4. Select Define a policy…
5. On the Edit Policy page, you will see a number of check boxes – checking one expands the page with more details. There are different types of policies you can activate: labels, auditing, expiration, form conversion, barcodes. Check the one to enable labels.
6. Now you can define the settings you want – see picture. You can click on the Refresh button to check out your work before creating the policy.
7. Click OK to create the policy.
8. Test the policy by creating a document in the document library. You will notice that when you are going to save the document, Word will ask you whether you want to have the label inserted.
8. Click Yes and the label will be inserted
Cool, not? And it is very extensible. You can create your own custom policies using .NET.
You can find this article here.