You can easily drive to Seeheim-Jugenheim and parking is not a problem. Alternately, the local train from Darmstadt comes through with several stops through the area. Trains 6 or 8 will get you there.
For a download of the trainstops to Seeheim-Jugenheim, click here
We get to the vineyard by driving, you really need to drive slow as once we miss the entry and we have to drive back.