resexellence.com is a great place to get started. When I used OS 9 I made the folowing changes:
System get info image
Sytem error messages ... mostly insulting to my self
the spinning e in IE
and I made my own sound set...
made women's voice say:
"Welcome back" (startup)
"disk inserted" (disk mounts)
"disk ejected" (disk unmount)
"files removed" (trash)
"copying compleeted" (file copying)
the rest of the system sounds were the same platnum ones.
I think I did some other stuff to.. but I dont remember. I havent messed with OS X yet. I like the interface too much to mess with it yet. Ill do it when I get bord of it some day... if I get bord some day.
... PS.. if anyone want to check out my sound set... I can send it to you if you like.