How are you getting your files on the PC? There's normally two ways to do it: 1. copy the files 2. stream them and record them (just like you'd do with a VCR I guess).
1. is better because you're copying the files intact. If done that way you should get TOD files. 2.'s disadvantage is a. you may be recompressing the video (which could result in loss of quality), and b. if the processor of the receiving PC is too weak, or the bandwidth of the link (firewire, USB, whatever) is insufficient, you're going to get dropped frames (at worst it'll stall or freeze).
According to the manuals from here
http://camcorder.jvc.com/product.jsp...Id=141&page=10
you can only stream and record if you were using firewire. So I think it's good you're using USB. Question is, when using USB, are you trying to import via given software (powercinema NE according to the manual, or are you using some other means? BTW looking for an additional drive in Windows Explorer and copying the TOD files from there to your hard drive should be fine too.
Lastly, it could simply be your PC is underpowered. Right-click your taskbar and pick task manager, then look at the performance tab. Then play your video. Does CPU usage jump to 100% while frames get dropped and the PC becomes unresponsive? If so, your CPU is underpowered. HD video is very processor-intensive. There's not much that can be done besides get a better processor. As a last shot, try VLC Media Player (
http://www.videolan.org). Some the bundled decoder in VLC might play it with less of a hit on CPU usage.