The Vixpa theme for Firefox is an attempt to refresh the Windows XP-style icons with the more polished Windows Vista feeling.  Your not getting the same old icons though.  All icons have been redrawn from the ground up, with a few original icons to replace those of XP’s. 

Here you have Vixpa with the normal sized icons:

Here you have Vixpa with the small sized icons:

Well worth checking out if you are missing that old Windows XP look and feel.  You can download the Vixpa theme over at the Firefox Add-ons web site.