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
- File-> New-> Search Folder
- Select “Create a custom Search Folder” which is at the bottom of the list
- Press “Choose”
- Give the folder a name e.g. “Drafts”
- Press “Browse…”
- Deselect the root folder and make sure only the “Drafts” folder is selected
- Press OK to return to the “Custom Search Folder” dialog
- 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!