You should literally bid on thousands of keywords for ppc to work good. This means any different combination of words and spellings you can dream up. You have nothing to lose. If noone clicks on it then you don't pay anyway so why not? This is a lot harder to do with google than overture. Overture's suggestion tool is a very valuable tool. It gives all the sub terms for a popular keyword and tells you how many times it was searched for last month. If you haven't used it you should start.
http://inventory.overture.com/d/searchinventory/suggestion/
Shane H
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