Tux Paint has a better UI than GIMP

It's true.

Have you tryed Paint.Net?

http://www.getpaint.net/index.html
http://www.getpaint.net/redirect/mirror_300_alpha1_betanews.html

Minimum System

    * Windows XP (SP2 or later),
         or Windows Vista,
         or Windows Server 2003 (SP1 or later)
    * .NET Framework 2.0
    * 500 MHz processor (Recommended: 800 MHz or faster)
    * 256 MB RAM (Recommended: 512 MB or more)
    * 1024 x 768 screen resolution
    * 200+ MB hard drive space