Hi Lora-Kate -
I was just in the same situation. I purchased the VHS and then found out about the DVD player that is coming for Xmas so I simply emailed SNM directly and asked to switch over. Whoever takes care of customer service over there is top notch. My order was switched over, billed out to my credit card and confirmed within 24 hours. If you can swing the extra cash, DVD is the way to go.
Take good care-
Your friend in fitness-
Snickerdoodle. :-cool