Usually the author (that posted it on Dribbble) will have a description of how he likes the PSD to be used - ie: Not for redistribution or doesn't want to see it used and reposted on Dribbble etc.

Safest bet - contact the author directly and clarify. You can find their contact info through Dribbble.

Personally when I find resources I'd like to use (mainly non print, commercially), I contact the authors directly and offer to buy a license. Everyone's pretty open and friendly.