In Microsoft Office SharePoint Server 2007 there is an option called Manage Checked Out Files in the settings page of a document library. This title is a bit misleading because that is not exactly what that option allows you to do.
If you choose the manage checked out files option you may notice that the list is empty even though you have documents checked out. A small bit of text above the list explains the reason: “Use this page to manage files which have no checked in version”. This means that if you have versioning turned on and have at least one version of the document checked in the document will not show up in the list even if it is checked out.
If you want to see all documents in a library that are checked out you can create a custom view with a filter to show only documents where the field “Checked Out To” is not empty.