The only thing that would work for your needs are some type of cloud computing solution like MobileMe or DropBox to be honest, it's really that simple. About the only other thing you could do is have an external HD store your photos and music. However that would be a risky solution due having to take it with you when you take the notebook out not to mention it's lack of convenience. I'm not sure why you are opposed to DropBox perhaps you could elaborate?
Firewire is simply a method to move data using a physical connection. Think of it as a USB connection on steroids. USB transfers information at burst of up to 400 MPS where Firewire moves at a steady 400 MBS. Your iMac has a Firewire 800 connection which moves information at a steady 800 MBS therefore being orders of magnitude faster than USB and 2x faster than FW.
I'll be watching this thread to see if anyone else has some additional thoughts.
Roger