starway - 3:12 pm on Sep 9, 2002 (gmt 0)

If the posted code is for image rollover effect only, then it has a lot of useless rubbish.
All you need is this:

if (document.images)
document.images['purpose'].src = 'images/buttons/purpose_f2.gif'

Of course, it's probably a part of the complete script that serves for some other things. But if it's just for rollovers, remove everything except what I wrote here. You just don't need all the rest.