Hi everyone. Need some help please.

I noticed the other day a funny thing: I exported a version of a .CR2 file (picture of bare tree branches against the post-sunset sky) from LR3 to a folder on my desktop that I use for my Wallpapers. Upon display, I noticed "jaggies" along the edges of the tree branches. I exported in 100% quality JPEG (aroung 7 MB I think). I tried several version, first changing the output dpi, then zeroing the sharpening in the "Detail" panel, exporting TIF (no compression). Nothing seemed to help. The weird thing was, that when I used Windows Media Viewer (or whatever its called) to view the pic (jpeg), there were no jaggies (even zooming waaaay in) - only when I display to the desktop.

Any help would be appreciated.

Thanks a lot

Damian