If you would like to expand the keywords in your campaigns, there are a few ways to do this.
a) Go to the "Research" tab, enter a keyword or website and chose the language. Currently available is English (UK/US/Singapore/Canada) and French (Canada/France). The keyword suggestions will include last month's and the current month's impressions.
b) Go to any ad group, click on "Edit keywords" and then click on "Keyword research tools". Simply enter your word or phrase and click "Find keywords". You can either search for keywords containing a certain word/phrase, search a website or the destination URLs of your ads.
c) You can contact MSN and ask for a search in their "vertical keyword libraries". This can help you finding keywords that you might not have in your account yet.
Keep searching!