Katakana can also be used to emphasize words, kind of in the way that we use
italics, or
bold type in English.
There is an example of Katakana used for foreign words on this current Japanese advertisement here.
http://www.japannewbie.com/japanese_...kemon-manners/
An example of Katakana used for emphasis here. (風邪 has become カゼ)
http://www.japannewbie.com/japanese_...-is-your-cold/
Another here... きれい has become キレイ
http://www.japannewbie.com/japanese_...gue-with-breo/
Hope that helps!