You may want to try to reset IE7. Tools > Internet Options > Advaced Tab > Reset

Remove any browser add-ons or toolbars you may be running (google toolbar, yahoo toolbar, etc) using Add/Remove Programs in Control Panel. If you are still experiencing the lockups try loading internet explorer with no addons by clicking on Start>Programs>Accessories>System Tools>Internet Explorer(no addons) and see if it's still happening. Addons can be disabled by clicking on Tools>Manage Add-ons>Enable Or Disable Add-ons. If it's not add-ons the problem could be caused by any number of things, without more information it's hard to say. If your problem persists your event logs may tell you what caused the program to lock and exit. Event logs can be viewed by using the Event Viewer under Administrative Tools in the Control Panel. Application errors (in red) are your likely suspects. Good hunting..