Bob
"Auto" will set the leading as 120% of whichever point size you set for the type size.
Example:
12 pt. type в 120% = 14.4 pt. for leading. In other words, multiply the type point size by 1.2
If you want to adjust manually, a higher number for leading that what "Auto" calculates will move lines of type farther apart; a lower number moves them closer together.
Did a Gurgle-search using the terms:
photoshop type tool baseline
and the first result at the top of the list was a link all about PS 5.x Type tips.
<http://graphicssoft.about.com/od/photoshop/l/bllps506b.htm>