I want to use the blur filter from this page (http://www.lissaexplains.com/fun7.shtml) and put it in a style sheet so that the blur filters only comes on whe you hover on them. The problem is, that I have no clue of how I could do this.

I know it's possible, 'cause I've seen people with it somewhere on the internet. . . it's just I don't remember where. . .

just put everything thats inside the style="..." attribute on that page into your a:hover { ... } section of your CSS.