The default setting for an IMAP account in Outlook 2007 is to download only headers from the Inbox, but you can change that setting to make it download complete items instead. Follow these steps:

1. Press Ctrl+Alt+S to bring up the Send/Receive Settings dialog.
2. Select All Accounts (or the group that contains your IMAP account’s send/receive settings), and click Edit.
3. Under Accounts, select your IMAP account.
4. Under Receive mail items, select Use the custom behavior defined below.
5. Under Folder Options, select Inbox, then select Download complete item including attachments.
6. Click OK, then Close.

The next time Outlook performs a manual or automatic send/receive for that account, you should see full items download into the Inbox folder.