As far as I know the only way to do that is manually editing some config files, but it's easy.
Edit
~/.gtkrc.mine (or create it if it doesn't exist). Put this inside:
->If you want a background image:
CODE
pixmap_path /home/yourusername/images
style "rox" = "default"
{
bg_pixmap[NORMAL] = "roxfondo.png"
}
widget_class "*Collection*" style "rox"
Change the /home/yourusername/images to the actual path to the background image you want to use.
->Tool bar icons:
CODE
pixmap_path "/home/yourusername/icons"
style "normal" {
stock["gtk-close"] = {{"close-icon.png"}}
stock["gtk-go-up"] = {{"up-icon.png"}}
stock["gtk-home"] = {{"home-icon.png"}}
stock["gtk-refresh"] = {{"refresh-icon.png"}}
stock["gtk-zoom-in"] = {{"zoom-in-icon.png"}}
stock["gtk-zoom-fit"] = {{"zoom-fit-icon.png"}}
stock["gtk-jump-to"] = {{"jump-to-icon.png"}}
stock["gtk-sort-ascending"] = {{"sort-icon.png"}}
stock["gtk-help"] = {{"help-icon.png"}}
stock["rox-show-hidden"] = {{"hidden-icon.png"}}
stock["rox-show-details"] = {{"details-icon.png"}}
stock["rox-select"] = {{"select-icon.png"}}
}
widget "*" style "normal"
You'll have to modify the icons' names to match the ones you have.
Save that file and open
~/.gtkrc-2.0. Add this line if it doesn't exist:
CODE
include "/home/yourusername/.gtkrc.mine"
->To change the MIME icons you just have to put the icons inside the
~/Choices/MIME-icons/ directory. You can also change this icons for the Rox menu: right click some file -> file <whatever.something> -> Define icon (or something similar, my menus are in Spanish).