OUR LADY OF PERPETUAL MOTION:Madonna, who has reinvented herself a dozen times over the last two decades, sheds her skin again on her new tour, set to play six shows at Madison Square Garden starting Wednesday. The sing er’s hometown concerts will be a career retrospective illus trating her evolution from club girl to provocateur to interna tional icon. All that in two hours and enough costume changes to make Diana Ross green with envy. Concerts are set for 8 p.m. Wednesday, Thursday and June 20, 21, 23 and 24. Limited tickets, $50 to $305, are available for all per formances. Madison Square Garden, 32nd Street at Sev enth Avenue; (212) 465-6741.