OK it's a bit more tricky than that.
We had our G4powerbook repaired and backed up mail onto another mac. In the last 2 week we have recieved more mail on that mac from 3 different accounts.

now I need to transfer the new (last 2 weeks worth) of mail, back to the powerbook.

I don't want to take it all back since the old mail is already there.

How do I go about this?

Thanks

All the new mail is in the inbox. the old mail in seperate folders. is there a way to copy the whole inbox aqmd the integrate it with the origional inbox on the laptop?

You might be able to use the redirect button and redirect it to your mac that you want it on.