Thank you all for your help.
Like Bruce mentioned it should be the XP / Firewire issue limiting the speed to 100 Mbps.
I digged a bit deeper on the forum and found out a thead with similar pbs:
http://forums.ni.com/ni/board/message?board.id=200&thread.id=16799
Go there to see a detailed description on how to solve the problem (an extra thx to
doelab
).
The AVT support is also very responsive: they sent me a tool for which makes it easy to downgrade drivers under XP SP2 !
regards,
Jean-Philippe