Van Winden's Garden Center is no ordinary nursery. More accurately, it's a two-acre amusement park for horticulture enthusiasts, offering over 300 varieties of roses, a mini-forest of Japanese maple and other trees. In the words of owner, Peter Van Winden, ''if it has roots, we have it.'' The impressive collection makes for not only a great shopping experience, but also a peaceful afternoon stroll. And it all started 50 years ago - the seed of the great American dream. There is also statuary, pottery, outdoor furniture and a range of gardening accessories in the gift shop.