I migrated a Portal Site from Sharepoint 2003 to 2007 using
SharePoint 2003 to MOSS 2007 Upgrade: Database migration « farhanfaiz’s Weblog – SharePoint / MOSS as a guide.
We have one remaining known issue. When we create a new list item or edit an existing Item, the field list does not appear in the sort order we have selected at List Settings - Column Ordering.