Well allthough this does not seem to be a vbgallery issue..(wrong forum?) just consider following when you replace gif with transparent png!!!
In the office i surf on a windows 2000 server box.. its old but works for us.. but i only have IE6 installed... not a major problem.. gets me to see all the major pages i want.
BUT IE6 does not support png transparency !!!
so for users like me.. please add a ie6 png transparency fix to your page... (you find a series of fixes on google search)
To test if it works .. install "the ie collection" on your machine.. (better than multiple ies) you can then check your pages in ALL versions of IE... including IE6 http://finalbuilds.edskes.net/iecollection.htm