Commerce Server 2007 with Service Pack 2 installed is now officially supported running on SQL Server 2008. Unless you are using Data Warehouse and Analytics, there are no special steps or requirements.
If you are using Data Warehouse and Analytics, the following steps MUST be performed prior to attempting to run an unPuP operation and configure the Data Warehouse resource:
After steps 2-4 are completed, the unPuP and configuration of DW/A feature-set will work without issue. The installation order for steps 2-4 is imperative.
Please visit the Commerce Server Community to engage in forum discussions, troubleshooting and support.