alias get.res { return $+($window(-1).w,x,$window(-1).h)  }

alias blue.side.f {
  var %res = $get.res
  if (%res == 1600x1200) { return Vtec Sidebar.jpg }
  elseif (%res == 1280x1024) { return Vtec Sidebar12by10.jpg }
  else { return Vtec Sidebar10by7.jpg }

alias {
  var %res = $get.res
  if (%res == 1600x1200) { return Vtec Topbar.jpg }
  elseif (%res == 1280x1024) { return Vtec Topbar12by10.jpg }
  else { return Vtec Topbar10by7.jpg }

alias { background [color:red]-l[/color] $ }
alias blue.side { background [color:red]-h[/color] $blue.side.f }

change these as follows:
[for the sidebar if you want it filled, stretched, etc. add the letter to -h. example: -hf to make it filled]
-cfnrtp = center, fill, normal, stretch, tile, photo
[for the 'top' depending if it's buttons, change -l to -u]
-l = toolbar
-u = toolbar buttons

This will only choose between 1600x1200,1280x1024, and 1024x768. If you want it to go lower you will need to add 'elseif' statements based on the examples, and change the final 'else' statement to reflect the lowest resolution image.

hope this helps,