Des scénarios de migration sont bien entendus prévus (ils ne sont pas encore finalisés du fait que Forefront TMG est encore en beta), aujourd’hui seule la migration depuis ISA Server 2006 est possible 

• Migration is supported only from ISA Server 2006 Standard Edition. Migration from ISA Server 2000, ISA Server 2004 Standard Edition, ISA Server 2004 Enterprise Edition, or ISA Server 2006 Enterprise Edition is not supported.
• Migration of settings from ISA Server 2006 Standard Edition running in workgroup mode is not supported. The ISA Server 2006 Standard Edition computer from which configuration settings are exported must be a domain member.
• Features provided by the ISA Server 2006 Supportability Pack will not be available after migration.
• If you have enabled the Local Host network to listen for Web proxy client requests, this setting is not migrated.
• Customized log field selections are not migrated. When ISA Server 2006 configuration settings are imported, customized log field selections are overwritten with default log field settings.
• Report configuration settings are not migrated.
• If you have specified a custom value for the number of times that an event must occur before an alert is triggered, this custom value is not migrated.
• If you are running a third-party add-in for ISA Server 2006, contact the vendor in order to check on the availability of an updated version for Forefront TMG.

Plus d’informations à l’adresse suivante : http://technet.microsoft.com/en-us/library/dd440998.aspx

Migration depuis ISA Server 2006 : http://technet.microsoft.com/en-us/library/dd440994.aspx