A firewire question

[Onkel Dunkel]

I?m considering buying an Asus A6Ja notebook that i?m gonna use for music (and other stuff) and i will therefore need a firewire audio interface. I want it to be 100% portable so the interface has to get it?s power from the laptop. Now the problem is that on almost all laptops the built in firewire ports are the type with 4 pins and as far as i know only firewire ports with 6 pins has power supply. This means that i can?t run firewire equipment that doesn?t have a powersupply of it?s own right? Now i?ve seen that you can buy a card bus adapter with 6-pin firewire (see picture below). Can i just buy one of these and all trouble solved? Will the audio interface eat the battery in no time? What do all you guys with laptops do?