Since JiK isn't around to give the 'definitive answer' :-P, I'll have a guess.

Woeking backwards, since moving it to the other port makes it work, then the OS is 'finding it' (attaching drivers, etc properly) the way it is intended to.

So therefore the first port is somehoew 'not initialised properly'... something you have probably already guessed...

Have you tried looking at the list of hardware (I'm currently on a linux box, so cannot remember how you get to there in the menu system!) and see if the firewire port is not initialised properly?

I'm not familar with either XP, Nero, or firewire, so I guess I'll have to leave it to JiK...