For some strange reason there the Reading Pane is not available for the Drafts folder in Outlook 2003. If you really need to have a Reading Pane in the Drafts folder you can create a Search Folder to workaround the issue.

Create a Search Folder for the Drafts folder

1. File-> New-> Search Folder
2. Select “Create a custom Search Folder” which is at the bottom of the list
3. Press “Choose”
4. Give the folder a name e.g. “Drafts”
5. Press “Browse…”
6. Deselect the root folder and make sure only the “Drafts” folder is selected
7. Press OK to return to the “Custom Search Folder” dialog
8. Press OK and press Yes again to close the notification

You now have created a Draft folder for which you can enable the Reading Pane!