You'll only find a video_ts folder on a proper DVD Video disc.
WMVs are computer video files that are stored on DVD data discs.
You don't need to compress them to copy the disc.
You can even copy the files directly to your hard drive in Windows Explorer and either watch them from there or burn them to another blank DVD.
In ImgBurn all you do is insert your original disc, select 'Create image file from disc'.
Then put in a blank disc and select 'Write image file to disc'.