See here. Excerpts:
According to Wisconsin campaign finance filings, Walker's gubernatorial campaign received $43,000 from the Koch Industries PAC during the 2010 election. That donation was his campaign's second-highest, behind $43,125 in contributions from housing and realtor groups in Wisconsin. The Koch's PAC also helped Walker via a familiar and much-used politicial maneuver designed to allow donors to skirt campaign finance limits. The PAC gave $1 million to the Republican Governors Association, which in turn spent $65,000 on independent expenditures to support Walker. The RGA also spent a whopping $3.4 million on TV ads and mailers attacking Walker's opponent, Milwaukee Mayor Tom Barrett. Walker ended up beating Barrett by 5 points. The Koch money, no doubt, helped greatly.
The Kochs also assisted Walker's current GOP allies in the fight against the public-sector unions. Last year, Republicans took control of the both houses of the Wisconsin state legislature, which has made Walker's assault on these unions possible. And according to data from the Wisconsin Democracy Campaign, the Koch Industries PAC spent $6,500 in support of 16 Wisconsin Republican state legislative candidates, who each won his or her election.
This is a useful piece as well.