One of the first technologies I used in my early SQL Server days were linked servers. I used them to migrate data from Ingres to SQL Server.
Yesterday Michel Ulens gave an excellent presentation on this topic on our latest SQLUG.BE event. Michel will be presenting the same presentation on the upcoming SQL Connections convention in Orlando. If you are lucky to attend this event, make sure to mark Michel's session in your agenda. For the rest of us, keep an eye the SQLUG.BE website, we will be posting the PPT and scripts soon.