Online investment bank Wit Capital Group Inc. snapped up its rival, E*Offering L.L.C., New York, for $328 million in stock. Online brokerage giant E*Trade Group, Menlo Park, Calif., will acquire Wit's retail brokerage accounts as part of the deal. (E*Trade own 28% of E*Offering.) Wit Capital, New York, is quietly building its clout in the online investment banking field. In January it merged with Soundview Technology Group Inc., a Stamford, Conn.-based tech investment banking firm.