A certain tension is in the air in Berlin. The winter has been gray and tepid. Spring puts out teasing tendrils, but has not yet sprung. The Berlin Biennale opens its fifth installment on Apr. 5, 2008, an extravaganza titled "When Things Cast No Shadow." Co-curated by Adam Szymczyk and Elena Filipovic, the show spans generations, nationalities and exhibition venues, including Kunst-Werke Institute of Contemporary Art and the Neue Nationalgalerie. And about a month later Berlin hosts its largest "Gallery Weekend" ever, with 34 galleries participating, up from 20 in 2005. The dealers hope to attract international collectors to see and buy. The back-room scurrying is palpable.