The forecast for Silicon Valley? More pain.

That’s because the fourth quarter registered another shutout for venture backed initial public offerings and the six recorded for all of 2008 were the fewest since 1971. Little relief was found in mergers and acquisitions, where the $13.9 billion valuation for the year’s deals was the lowest since the $7.5 billion recorded in 2003.

The tally from the Exit Poll by Thomson Reuters and the National Venture Capital Association suggest tough times ahead for venture capitalists.

“The inability of our strongest companies to go public and the softening of acquisitions activity continue to have a major ripple effect that now reaches every stage of the venture investment lifecycle,” Mark Heesen, president of the NVCA, said in a statement. “As a result, new investments and fundraising will slow considerably in 2009 until the exit markets re-open and the pipeline is cleared.”

The report found that 28 venture-backed companies are in registration with the U.S. Securities and Exchange Commission, 10 fewer than in the third quarter.

In a lean year, the top IPO was the debut of Rackspace Hosting in August, which raised $187.5 million. The year’s No. 1 M&A transaction was Dell’s acquisition of EqualLogic for $1.4 billion in January.

The study found that 46 percent of M&A transactions returned more than four times the venture financing in 2008 versus 41 percent the prior year and 28 percent of deals