WHEN HE started the now-defunct Galaxie 500, singer/songwriter Dean Wareham avowed unfamiliarity with the Velvet Underground. Since founding Luna, however, he's forsaken such claims: Lou Reed's "Ride Into the Sun" has been central to the New York quartet's sets, the band opened for the Velvets on their 1993 European reunion tour and now Velvet guitarist Sterling Morrison plays on two songs on the band's second album, "Bewitched."