Hi there,

Did you install appropriate MS Office updates? If not, please install the update 933493 which resolves the performance issues and improves the general responsiveness of Outlook 2007 during common operations.
Update for Outlook 2007 (KB933493)

If this can't help, run the Outlook in safe mode.

1. Quit Outlook. Click Start menu, and click Run.
2. In the Open box, type: "Outlook /safe" (without the quotation marks).
3. Click OK. Is Outlook working fine under Outlook safe mode?

If the problem doesn't occur under Outlook safe mode, please restart Outlook in normal mode and remove COM Add-Ins.