I think a good idea is to build a Webpart so as to export 2003 Lists & Libraries to 2007.

Wouldn't this be done during the process of upgrading the Sharepoint site or is this something where you would just want to export the list from 2003 and then move it to 2007? I guess my questions come in when we would start looking at documents or image libraries etc... For example if you were exporting a list or library of 'quote of the day' this wouldn't be a big deal but if you wanted to export a document library this would be more difficult.