Is Dan Rather Joining Tina Brown's New Venture?Dan Rather's contract with Mark Cuban's TV network HDNet should not be up until nearly a year from now, assuming the terms Rather disclosed just before he inked the deal still hold. But would the contract prevent the former CBS Evening News anchor from contributing in some way to Tina Brown's forthcoming news website The Beast? Perhaps that's what Brown and Rather were discussing during a "very long lunch" at The Park on Tenth Avenue, as reported by a Post spy. Though Rather's work at HDNet has garnered some positive recognition, it's not nearly as visible as his work for CBS was. A Web gig or partnership would give Rather a shot at regaining more of the attention he once had — and that any veteran TV newsman would crave. Perhaps the skilled lawyers working for Brown's business partner Barry Diller can work something out on the proud old newshound's behalf. [Post]