Optimizing for Yahoo

[Maddy]

My new client is well optimized for Google. I did a check on their clicked keywords for search engine and positioning and found that none of their organic traffic is coming from Yahoo! Also that none of the keywords that are coming up well in Google are coming up at all in Yahoo. 1 in about 100 are actually coming up in MSN as well as Google but Yahoo is coming out a big zip! Anyone ever see this before? Any suggestions on how to optimize for Yahoo without Killing the Google Listings?