Globalsign certificate is showing in MAC Keychain after installation. But not importing in Entourage.
The first option would be to make sure you have the correct format for the certificate. You might only have the public key file. You need both the public and private keys stored in the file. The certificate to import to the keychain access needs to be in the format PFX or P12 file extension formats (eg. yourcert.pfx). In the Keychain Access when you import you should see a small arrow next to your certificate shown in the keychain. Click on this to expand and then underneath will be the private key shown. If you do have this option to expand the certificate details this is definitely where the issue is.
You will need to export the certificate again from the original location, making sure you export with the private key, or you can reissue the certificate through your GlobalSign Account to receive a new certificate with the public and private keys. You can do this on your MAC through Safari and choose the option to receive in PKCS12 format. This will not affect your current certificate if installed on another machine.