You know you can get (quite cheaply now too!) combined video and DVD recorders, which enable you to copy with one button from one to the other and vice versa.
Other than that, surely it's a question of having the right outputs, inputs and leads if you have seperate machines.
i think you may have to have a switchboard that contains an input/output control for each device (you can get one from agros for �9.99) and put the VHS onto output and DVD onto input and press record on the corresponding machine and vice versa
Ethel is correct.
You can connect the VHS to the DVD recorder with a normal scart lead, and off you go (assuming that there's no copy protection on the video tape - then it's gets a bit more complicated, but is still do-able)