neway, in respect 2 wht ppl sed earlier about barres bein painful, i suggest that it isnt always required 4 a full barre 2 b used. only apply pressure where required, and try 2 get the creases in your finger at the rite point. i hadnt come across barres 2 much, until i learnt mason williams' classical gas (beautiful piece), which has a "difficult" barre part in the middle. once barres have been mastered, they are incredibly useful tools.
futhermore, use the weight of your hand along with gravity rather than muscles in your hand 2 help provide adequate pressure 4 a successful barre