Those cables are USB and are for transferring stills/jpegs to Mac.
For capturing your HDV/DV from tape you need FireWire.
Your old Mac has both 6 pin and 9 pin FireWire ports.

If you have not already got a FireWire cable then I would suggest you get the 4 pin to 9 pin FireWire cable which will set you back only a few £$.
The cable will look like this.

The 4 pin end goes into the DV/HDV port on the cam just above the HDMI outlet,under the cover. The 4 pin end is quite small so don't force it into the cam' the wrong way round.
What iMovie version do you have on the old Mac and what OS ?
Once you have captured the footage onto old Mac you may want to transfer it over to new Mac.