. . . now may be the time to do it. Brandeis has just opened a new exhibit of highlights of the collection that the administration may, or may not, be in the process of selling. So is the current show evidence that "the Rose is open," as Brandeis would have it - or your last chance to catch an eyeful of the university's deKoonings, Rauschenbergs and Warhols? You decide! Greg Cook reports.