That kind of GUI is called a desktop environment. Before OS developers do anything nifty, we usually spend a lot of time working on the core of the operating system (mostly the kernel). Also, you'll need to settle a way for controlling the screen display, whether by oldschool VGA, graphics card utilization or whatever method is the most practical for your purposes and ability.
When you're ready, you can try following something like this tutorial:
http://www.brokenthorn.com/Resources/OSDevVga.html
Unless you're stubborn and the "elite-breed", you'll remain simple and cope with the limitations of old video modes until you gain the ability to control (atleast) your own graphics card model. The amount of complications involved with supporting more hardware (i.e the variety of graphics cards etc.) will get ugly.
Some day, you might be able to (after some challenge) create a low-color-depth desktop environment with support for little icons and stuff. The icons can be created with an image program which supports the kind of color depth you want. You can study these simple image formats (such as BMP, ICO, GIF etc.) and maybe implement them directly into your operating system, or you can make a program which converts them into a custom image format of your own design.
When life gives you lemmings, keep them safe.