By vts files I am guessing that you mean files with a file name Of vts_?.vob (the extention is vob)? I'm also guessing that you want to make a standard dvd movie that will play in a normal dvd player?vts_?.vob files are dvd video files but are only designed to work with the corect support files. If you have the original dvd, then copying it is no problem with the right software. If you do not have the original dvd, do you have just the vob files or do you also have the support files too? If all the files are there, then again it is not a problem. Several programs such as dvd decryptor, nero recode etc. can take an original dvd or a folder withh all the files that were on an original dvd and burn a dvd.
If you only have the vob files, then you are going to have to recreate menu and support files to make a standard dvd video disk. I'm not farmiliar with cucusoft, but if it is not capable of dealing with vts_?.vob files, then change the file extention from vob to mpg. Vob files are just standard mpeg files. The file extention has been changed to work with dvd, but they require the right support files. After you have changed it to mpg, the software you are using should be able to use them. There are other options too. If you have nero6/7, nerovision express can take the vts_?.vob files and assemble new support files with new menus. In nero, do not change the file extention. If you give nero mpeg files, it reencodes them which takes hours. If you give it .vob files, it can often assemble them and add menus, without reencoding. Look for the make your own dvd video option in nero. Alternativlly, you can look for authoring software here.
Most dvd authoring software should be able to make a dvd out of vob files.