You have to be cautious to avoid copyright infringement. If what you intend to do is to take content that individuals have taped and convert it to a DVD for their own use, you won't have a problem. But if what you want to do is to obtain VHS commercial movies, convert them to DVD and sell DVD copies of those movies, you will undoubtedly violate the rights of the holders of the copyrights on those movies.
Disclaimer: This general information is not intended to give rise to an attorney-client relationship. I am not licensed to practice in Iowa.
No. If you can even find VHS copies, it's very likely that the copyright owners of the content on those VHS tapes will sue you if you copy their films onto another format and sell them. Copyright owners own the exclusive right to reproduce their property, and they've very likely licensed the DVD distribution rights to another user, whose rights you'd also be infringing by your intended (mis)use.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
Yes, it is illegal.
When you buy a VHS you actually buy two things: 1. the plastic enclosure and magnetic tape, and 2. a non-transferable license to play the contents in a VHS reading machine.
By transferring the VHS contents into a DVD you are in probable violation of the license. By making copies, in any format, you are probably in violation of the license.
So, don't do it