<BLOCKQUOTE><font size="1"face="Geneva, Verdana, Arial">code:</font><HR><pre><font size=1 face=courier>
tell application <font color = red>"Finder"</font> to set the desktop picture to <font color = red>"Frunse:Users:seb

ictures:Hirn.tif"</font>
</font>[/code]
where "Frunse..." is the path to a picture on my hd. i left it in there to show the kind of colon separated path it requires.
use
<BLOCKQUOTE><font size="1"face="Geneva, Verdana, Arial">code:</font><HR><pre><font size=1 face=courier>
osascript -e 'tell application <font color = red>"Finder"</font> to set the desktop picture to <font color = red>"Frunse:Users:seb

ictures:Hirn.tif"</font>'
</font>[/code]
if you want to embed it in a shell script or an nstask.