As far as resolution, I do all my work in 300 ppi, unless it is for the web, then 72 ppi

Here is a good tutorial for painting hair.  It's a long one though, be forwarned.
http://www.renderosity.com/mod/tutorial/index.php?tutorial_id=125&page=1

And here is another one that might help you...
http://www.renderosity.com/mod/tutorial/index.php?tutorial_id=87

Have fun!