I believe it's found in
this file. You'd have to replace it with a currently existing one. You'll have to edit the logo to make it what you want, as well as make the background transparent. Plus you'd have to resize the logo to the proper size. I'd suggest
GIMP.
When your done, you'd either have to put the finished pac file in the
pf > Menu2 folder, or place it in a
common5.pac which goes in
pf > system.