For those of you unfamiliar with the wonders of digital painting in Photoshop (LAYERS rule baby!) the digital painting forum I belong to has been promoting this free ONLINE painting software called SUMO Paint.
It's almost the exact same as the ancient version of Photoshop 7 that I use, all the buttons and thingies are in the same places, there's layers (woop woop!). The only thing I've found so far that sucks is the top image size is 2880 x 2880 pixels and I assume at 72 DPI resolution and you can't create custom brushes like in PS other than that, it's a great intro to digital painting - for free. It's not a download though so you gotta use it online but you can save (and print) and email your art around. When you leave the site it's like closing PS, asking if you wanna save your work. Work can be saved (and re-imported) from your hard drive or saved at an account on their site.
As with any painting program, using a Wacom or other pen tablet to control your digital brushes is way better than a mouse. I tried mine on it and it works great.
Have fun, if that's the sort of thing you like to do!