Outlook 2007 will block scripts/macros if they are not digitally signed. However, you can create your own digital signature and assign it to your script to prevent outlook from blocking it on startup.

From your start menu search for Digital Certificates and you will see a program called Digital Certificates for VBA projects, run that and create a name for your certificate.

Inside Outlook, open the code editor and your code open select the Tools menu and then Digital Signatures. Select your signature just created and click "click here to view certificate properties", click "Install Certificate", Click OK then OK again.

Save your script again and close the editor window and Outlook saving the VBA script if prompted.

Reopen Outlook and when prompted about the certificate select "Trust all documents from this publisher" - the publisher being the certificate you just created so dont worry

All done, enjoy.