Sort of.
... What he actually did was send ATR's president, Grover Norquist, a letter essentially stating he supports the pledge, without actually signing it. I believe this was the same thing George W. Bush did in 2000.
Does it count? You bet. An ATR spokesman told me:
"ATR considers Rudy's statement in writing to achieve both the spirit and the letter of the Pledge. We are moving him into that column."
This now leaves only Fred Thompson and John McCain as the remaining GOP candidates who refuse to forswear tax hikes.
Taxes are a big issue in New Hampshire, so it's no surprise Rudy decided to sign the no tax pledge.