I have a 15GB list with attachments that I need to migrate from SP2003 to SP2007. Can anyone suggest a solution which will keep my list and attachments intact?
i think you can use the migrate content database approach. check this technet:
or i would recommend to buy a 3rd party tool to migration. As per my personal experience i would recommend ShareGate.
OR there are several other tools available in market Tsunami migration tool QUEST AVEPOINT METALOGIX