If you insist burning VIDEO_TS folder (you do not need AUDIO_TS, it's empty), than copy that from DVD like any other file/folder to hard drive. If DVD is protected (all commercial are), than you have to rip it to HD.
Than in ImgBurn, on start up page, click on File/Folder to Disc, find your VIDEO_TS folder, and burn.
There is one think which can happen, place DVD disk in drive before locating VIDEO_TS folder, otherwise ImgBurn can get stuck. It happened to me on few occasions.