I've just had the same problem...
I've read as many posts as possible on this topic on various fora but havent found a satisfying answer. I still have to find a sp1.cab for the retrieval of the ohci files and try that fix. In the meantime, i found a different temporary solution that i have used for several times now and does the trick everytime!

When my camera stopped being recognised, i removed the firewire cable and i shut down the IEEE1394 interfaces in the device manager. Next i switched them back on and replugged my cam. Untill now, he gets recognized on the fly everytime...

Not the cleanest solution but it satisfies my current needs...

Hope this procedure helps others to overcome this irritating driver bug...

Greetz from digital videoland...

Me