Microsoft has spotty support for 1394 (FireWire, iLINK) in its Vista and XP OSes.
Win7 (finally) has solid support (have not heard issues to date, but no guarantee).
Some related links that may help:
Vista and XP in Wikipedia
Performance of 1394 devices may decrease after you install Windows XP Service Pack 2
And remeber, you MUST use a 6 or 9 wire connector. The tiny 4 wire sockets do not work with the Extreme.