Question about desktop pictures...

Hey all...this has really been bugging me, and I have not been able to make any progress...

Is there a way to change how OS X positions desktop pictures that are not the same size as the screen resolution? Right now, the default is to tile the pic, whereas I would prefer it just to center one copy of the pic and have a solid background color surrounding it (preferably black). I tried messing with some of the options in, but nothing seemed to work (or even happen at all).
/System/Library/Preferences/Appearance did not seem to have anything either. I'm not sure where else to look. Any ideas? I would hope for at least this small degree of customizability. Also, is there even a way to turn off the desktop picture? (besides setting a corrupt file as the picture). And finally, is there a way to edit that solid background color?

I realize that I could possibly just take all of my current desktop pictures and make their entire size match my monitor, but that is a pain. Not to mention I often come across pictures that I like to use for my desktop, and to have to constantly edit these pictures would be annoying as well. So, I (and I am sure others) would prefer a slightly easier method.

Any help that you can offer would be most appreciated. Thanks.
I have a dual monitor setup and I was trying to figure out how to put seperate pictures on each one. As far as I can tell, this is not possible.

I even tried making one super-wide image to fit across both, but it stupidly squished a copy on each monitor.

This is clearly not something the OS X/Unix folks spent much time one. I expect we'll see this fixed once the OS 9 folks are freed up to work on OS X...
Yes and no...

If you open the desktop plist in your preferences folder there is a line that says <key>position</key>

you can change that automatic to Centered (I've also gotten Scale to work) or Tiled. My problem is that I can't figure out how to change the default color that shows through if your image isn't big enough to cover the whole screen. I sure wish there were an easy "scale to fit" command, but I don't know what that would be.