Can you pinpoint when this is happening? Are you trying to do something specific each time this occurs? Try to monitor your memory while on Outlook and see if your memory level is low at the time it fails. Open the Task Manager and choose the Performance tab to get a graphical view of the CPU and Memory usage. Keep this window open while on Outlook.
Also be sure all unneccesary windows are closed and are not running on the bottom of your desktop on the taskbar.
You can try to uninstall/reinstall Outlook from Control Panel/Add Remove Programs (left panel -- Windows features)
I hope some of these sugestions will prove helpful.