A word of caution -
Just because an accounting firm suggests that you may be eligible for 'found' money does not mean its free or easy. My firm was approached in 2008 with a pitch very similar to this, and it sounded quite reasonable and intriguing. We signed an agreement with the CPA (they collect up to 50% of all 'found' money, hence their interest) and filed amended tax returns to claim these credits. We were shortly hit with a full IRS audit and subsequent denial of our petition.
At the end of the day, we were out the prep fees (for amended returns) to the CPA, additional audit fees to our own CPA and 100+ hours of staff time. Your experience may vary from this, but I suggest you be wary of CPA's bearing gifts.
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Peter Saucerman AIA
Dreyfuss & Blackford Architects
Sacramento CA
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