TwistedBrush Open Studio is a nicely featured art and painting program which comes with a large selection of brushes to make your Picasso moment come alive. The interface is a little 1980s, but it seems to have everything you require to create artistic finery. As with all of this genre, you really need some sort of tablet add-on to use it properly, as mouse and keyboards tend to suck the creativity out of your body pretty quickly.
TwistedBrush runs on all versions of the Windows operating system and is designed for all realms of digital art including natural media fine art, photo retouching, photo composition, photo cloning to turn your photos into the look of hand painted artwork, mandala art, patterns, manga, even 3D like painting with the incredible blob modeling tools.