I have been using the data loader to migrate Account, Opp & Contact data across from once instance of SFDC to another.

However where I need advice is around Activities, Tasks, historical e-mail, attachments, etc. (1) How / what format do I need to extract this data in from the original instance/ (2) What is then the best way to import this into the new instance?

From a few simple searches so far Jitterbit seems to be a tool of choice, but it's not clear if there are other options or even if this will satisfy the requirements. Any advice would be much appreciated....