To change system icons like trash you're going to need an app that'll do it for you. There are two different ones I'd recommend, first is Candybar which is a shareware app chock full of options that'll allow you to replace system icons, default folder icons and mod your leopard dock. If you don't need so many options and just want to change the trash icons, you can use LiteIcon which is freeware and will give you options to change and restore system icons. Hope this helps