If a Macro has been digitally signed and you have added this signature to your excel "trusted sources" under the macro menu you should be able to run a macro without being prompted.
Create your own digital signature
Create your own digital certificate
Run the Office 2000 setup program again.
On the Select Features screen in the setup program, expand Office Tools.
Select Digital Signature for VBA projects, click the arrow next to your selection, and then select Run from My Computer.
In Windows Explorer, locate and then double-click the file SelfCert.exe in C:Program FilesMicrosoft OfficeOffice.
Note Because a digital certificate that you create yourself isn’t issued by a formal certification authority, macro projects that are signed by using such a certificate are referred to as self-signed projects. Depending on how your organization uses the digital-signature features in Microsoft Office, you might be prevented from using such a certificate, and other users might not be able to run self-signed macros for security reasons. Learn about digital signatures.
For more information about creating digital certificates, see Help in Visual Basic for Applications.
( source excel help)
Digitally sign a macro project
Make sure you have at least one digital certificate before you try to sign a macro project
Open the workbook or template that contains the macro project you want to sign.
On the Tools menu, point to Macro, and then click Visual Basic Editor.
In the Project Explorer, click the project you want to sign.
On the Tools menu, click Digital Signatures.
Do one of the following:
To use the current certificate, click OK.
To use a different certificate, click Choose, select the certificate you want, click OK, and then click OK again.
More information
Learn about digital signatures
Learn about how security levels and digital signatures work together
( source excel help files)
Setting Security Levels in Office Applications
(source :http://www.microsoft.com/office/ork/2000/three/65ct_4.htm)