If it has an ExpressCard or PCMCIA expansion slot, then there are firewire cards available. Examples:
If it has neither of those, but has a Thunderbolt port, then the Thunderbolt to firewire adapter cables work great.
As R. Proffit indicated, USB-to-firewire cable/adapter/converter things will not do the job, so don't waste your money or time.
An external drive with multiple connection options generally will not act as a passthrough from one technology to another. If the USB port is connected to the computer, the USB connection takes precedence and the other ports (firewire, ethernet, SATA or whatever) will not be active.
My camcorder has a DV output and I have a DV to Firewire 400 cable. My old pc had a firewire port so no problem. But my laptop doesn't have one. So I bought an external hard drive that has a firewire port, connected it to my laptop and then connected the camcorder to the external hard drive. The problem is that neither my Ulead 11 program nor Windows Movie Maker will find the camcorder - only the webcam on the laptop! I copied the Ulead files to the external hard drive and then ran it from there, but still no luck. Does anyone have any idea how I can get the video from my camcorder to my laptop? Any help much appreciated! Thank you very much.