I have read a lot on this forum about problems with firewire, XP SP2 and Sony camcorders. I too had this frustrating problem, which has now been solved.
I recently bought an AMD64X2 4000+, 2Gb RAM, dual SATA disks, running Windows XP SP2 to further my video editing hobby. The problem I had was that the capturing software did not recognise the video device. I used the same Sony DCR-TRV830 camera and firewire cable on my old Windows ME PC and this worked well (albeit rather slowly).
I eventually solved the problem when I exchanged the firewire cards between the two PCs.
The 5 year old Belkin F5U501 Rev 1.4 firewire card immediately detected the video device and I had no prolem with capturing. The new VIA VT6306 firewire card does not work with either XP or ME.
Hope this helps someone!