The lead refered to is the svideo lead, it has 4 pins and a plastic locating key in the connector, you should alredy have one for your svideo camera. It is the same lead you used to link the Svideo cam to the vcr, otherwise these are available almost anywhere even tesco, asda or B&Q or get 1 from
www.keene.co.uk
Your vcr and cam work in the same way, they both record to tape and play it back.
You say you have a new pc coming, if it is not to late it would be good get windows loaded on to a smaller drive of about 80Gb and keep the 200Gb just for video capture. This helps to share the load, no matter how fast your machine is, video editing and capture is hard work, but do not despair, it can be done with the 1 drive.
DV uses about 13 Gb's per hour of video, and of course it will use that amount again when you export your edited video back to the hard drive. Do it 1 tape at a time and transfer it to DVD then you can make space for the next one by deleting captured video you have just finished working on.
DVD uses MPEG2 video so you will have to encode your edited dv to mpeg2 and author it for DVD, This sounds scary doesn't it, but it really isn,t, reasonably cheap programs like Ulead videostudio do it all for you, there might even be some software with the camera, I don't know much about what JVC bundle with they're cams.
www.videohelp.com and these forums are great places to learn from
You mentioned your old machine as being only USB1, firewire and usb are not compatible, they are 2 different types of connection. the JVC may have a stills transfer and webcam transfer to usb, but for the digi video from the tape you need firewire.
Take it one step at a time, only worry about the step your on and don't look ahead to the next one til you get there.
You'll be fine.