Linux:
download .png files
updatedb && locate founder.png
mv /path-to-download/founder.png /path-to-located-file/
repeat for op.png and voice.png

Windows:
download .png files
Start, Search, Search for files or folders named: founder.png
Right click on /GAIM-path/founder.png and Open Containing Folder
Alt Tab back to search and Drag & Drop /path-of-download/founder.png to default folder, click yes to replace file.
repeat for op.png and voice.png