Besides the 4 match types ( exact, phrase, broad and negative) available in Google Adwords ( See Google Adwords Support. if you don't know them) available for ad targeting, there is also a less known one called "embedded match", which is a combination of match types.
Embedded match is a sophisticated form of keyword matching that allows you to prevent your ad from appearing in relation to certain phrase or exact matches. This is popular when an advertiser sells merchandise related to a movie or book, but not the actual movie or book.
Example: An advertiser selling Toy Story merchandise might use the embedded match option of a negative and exact match on -[Toy Story]. This way, the advertiser's ads appear for Toy Story dolls and Toy Story products, but not for the exact match Toy Story.
There is a great training video on embedded match techniques you can find on Stompernet.
The negative keyword forms were added if you want an easy way to convert the Google negative keyword format to MSN Adcenter or Yahoo Search Marketing.