Enlarging Icons on Vista 64 Ultimate?

Hello,

I am sure this question has been asked and answered before but this forum does not have a good search engne so I was unable to find the answer.  I apologize also if this is a n00be question for I am new to wincustomize.

I am running Vista Ultimate 64.  I am using IconPackager 4.0.  I downloaded and altered my icons with packages downloaded from WinCustomize.  First, the "use large icons" feature under settings in IconPackager is greyed out.  When I enlarge the icons using Crtl+Mouse Wheel all the default windows icons enlarge and the spaces between the icons enlarge/shrink but the custom icons that I have downloaded from WinCustomize do no grow though they will shrink.  So my question is: how do I get the custom icons to "grow?"  Do I need a special kind of icon to enable this feature, and if so how do I identify these icons on the WinCustomize library?

Thank you for any help you can offer to solve my dillema.