Most people seem to use the technique called "Smudge Painting" A quick google search should turn up several good tutorials.
In terms of hardware, I think it's safe to say that most use a tablet of some sort. It's possible without, but it certainly is easier with one.
Jason
P.S. Wacom's "Intuos" line of tablets includes painter essentials. Not as good as PainterX, I'm sure, but still worth thinking about if you're in the market for a tablet anyway.
P.P.S. Forgot to mention, a lot of people use specialized Photoshop brushes to help simulate different painting styles. You might want to search for them as well.
Greg, I agree with the advice that Jason has already given you. Additionally, there are a series of books, the "How to Wow Photoshop for Photography" which not only have excellent instructions but also come with a CD of a number of fine brushes in various media.
Greg, have to agree about the tablet. You can get by with using the mouse (I got pretty good with one because for years I could never afford a table the size I wanted), but in PS you can basicallly build a painting in layers over a photograph by using oil painting methods. Study those, convert the processes to PS and you'll do great.
Since I'm a filter guy, I'll pass on some of my favorite filters (that are free that is):
Impressionist (can get it still on Trimoon's (Steve's) website)
Eye Candy III (has lot's of cool effects that can be used in layer blends for oil renderings; note that Alien Skin does not support Eye Candy III anymore, but why should they)
Paint Engine (not there direct site, but this site has some cool presets so it is what I'm linking).
One of my favorite brush techniques is to combine PS's Angled Brushstrokes (run after adding a tiny bit of greyscale noise; you'll see why) and Eyecandy Jiggle (wide setting; gives that loose handbrushed feel).
Lylejk I was reading about Paint engine and I think you have to copy a ini. file on yor Windows folder, is that safe? I mean is there a chance of screwing things up?
I keep a subdirectory of differing settings (as you know, you only have a limited number of presets that you can use at any given time) that I change out with as needed (rarely do now since I currently have the ones that I mainly use in one group). Again, the preset .INI file needs to be in your C:\Windows directory (file name is fmachine.ini if you didn't know). To better answer your question, no it will not mess anything that's Windows related up and it must be located here by filter design unfortunately.
to post in this forum, but wanted expert advice.