As a former credit analyst, the best training i've seen has been through CFT (Center for Financial Training) http://www.cftusa.org/locquery.asp?area=WA
I started out as an assistant branch manager and went straight into credit analysis (commercial). I worked on the small stuff at first (<250,000) for the first few years, while my team leader trained me on the job. Probably the best training you can have is a HR Block corporate tax return training class. Just a review of how to read them and the workings of a balance sheet and income statement. The rest of commercial credit analysis is fairly straight forward in theory.
I atteneded a bank management class at Marquette that would have been a good foundation. It taught commercial credit analysis as well as introduced the idea of compensating balances, securitization, collateral valuation and many other things. I can't find a link to the book we used, but if you're interested pm me and i'll search harder and send you a link. It has the information to give you a good base to speak intellegently about credit analysis.