Did u mean Outlook 2007, if I am not wrong, then follow the steps to overcome this….
1. If files that u attach are zipped when u do not expect them to be, check to see whether a .zip utility has been installed in Outlook as a COM add-in.
1. On the Tools menu, click Trust Center, and then click Add-ins.
2. In the Manage list, click COM Add-Ins, and then click Go.
3. In the COM Add-ins dialog box, clear the check box next to the add-in name, and then click OK.