As far as I know there is no way to do it, unless there is some 3rd party software out there.
(Your not the first person asking this either... http://forum.soft32.com/win3/LOCK-DESKTOP-ICONS-PLACE-ftopict124471.html )
I have some alternatives...
Put your icons in a folder on the desktop, the layout in that folder window should stay the same. I used to keep my desktop cluttered with only a few spaces free on the entire screen, but now I put that excess in a "Stuff" folder, keeping my desktop clean and less embarrassing.)
Put your most used icons in the quick launch toolbar. You should not have any problem with those moving by themselves. If you do not have the quick launch, just right click on the taskbar then go to toolbars and enable it there. If you want to re-size the toolbar area you can do that if you unlock the taskbar (right click taskbar)
If you want to access programs easy, you could consider shortcut keys. Right click on a shortcut, then click into the shortcut key box and hit a shortcut key combination (Control + Alt + key / Control + Shift + key / Control + Alt + Shift + key)