It's hard out there for a Posh.Thanks to her fashion empire and very photogenic family , Victoria Beckham is pretty much on top of the world these days. But, it wasn't so long ago that she was a pop star who wasn't even allowed to sing at gigs. Oh, the indignity.While it's no secret that Posh Spice had fewer solos than her fellow Spice Girls during their '90s heyday, we didn't realise just how unwelcome her voice was. Appearing at last night's celebration for the "Vogue 100" exhibit at London's National Portrait Gallery, Beckham admitted that often her microphone wasn't even plugged in. Is it any wonder she's so reluctant to get the group back together?"They [producers] used to turn it off and just let the others sing," she told presenter Claudia Winkleman . "I got the last laugh — and now my mic is well and truly on, finally.”Way to make lemonade, V.B.