That is called the throbber and cannot be edited in SKS 6.. it can however in SKS5.

You can also google Throboff... a small app that removes it locally. in Explorer and IE

I was trying to crack this problem with one of my skins just this morning. I've d/l'd GT3 by Tiggz, the description of which says the throbber is replaced. The skin indeed has images for the small, medium & large throbbers but they don't get applied to Windows Explorer windows here. Same with the corresponding images I made for my skin. I can't find anyplace in SKS5 where you can 'toggle' this or otherwise enable use of the images.

A question occurs to me - assuming you can get throbber replacement to work in SKS5, will the functionality remain after subsequently editing the skin in SKS6?

I'd be very interested if anyone has gotten this to work, to hear how. If it doesn't actually work, ThrobOff sounds like the way to go, local though it may be. XPP SP2, current WB6 beta.