On a Windows 7 64bit, I was not able to capture any DV video from a video camera connected via Firewire IEEE1394. I was able to control the camera from the capture program (tried NeroVision and magix Video Deluxe) but only got a black screen and no audio.
After a little search, I found this forum post which suggests to switch the IEEE1394 driver from the automatically detected Texas Instruments one to the 1394 OHCI Compliant Host Controller (Legacy) one. After that change, everything worked as expected. This seems to only affect 64bit systems.
To switch the driver, do the following:
devmgmt.msc, click OK