For eyefinity it has to be active. If you're at 1920x1080 you only need a single link adapter (~$30) but for bigger resolution you need a dual link adapter which are usually $100 or more.
You might need to get a displayport to dvi adapter then use a dvi to vga adapter on top of that.
However, if you're only using 1 or 2 monitors you don't need an active adapter.