Hand positioning is very important in regards to being able to reach, stretch and curl your fingers. What I mean by that is if you position your guitar more like a classical player might do and keep your thumb behind your second finger then it will be easier to utilize the pinky finger (fourth finger). It's called keeping "square" to the fretboard.

As far as finger exercises I have a free eBook at my website (http://www.guitarlessonsbuffalony.com) available for download that goes over many different picking patterns and left permutations. If you have any questions feel free to contact me.

All the best,
Joe Pinnavaia
http://www.digital-nations/artists/testtuberhino
http://www.guitarlessonsbuffalony.com