They look different to me... one says 1394 on it, the other says USB.
You might as well add sugar to your car's gas tank, if you're going to plug the Firewire cable into the USB header.
The wire pinout on the USB cable is undoubtedly the typical
+5V . Data- . Data+ . Ground . Ground
+5V . Data- . Data+ . Ground
And the firewire cable would be
DataA- . Ground . DataB- . +12V . Ground
DataA+ . Ground . DataB+ . +12V
So if you match 'em up, then if you plug a Firewire device into a Firewire port that's attached to a USB header, your iPod (or whatever) will get hot 5-volt power on its twisted-pair-A data lines (bad!), and grounds on one of its two twisted-pair data cables and its 12V lines. So I believe you'd probably ruin the iPod point-blank. Possibly the motherboard too.