My question is this- I keep getting attacked by Flaming
Fist guards in Beregost .. my reputation is low ( am a neutral character) is this the reason and if so what is a good way to bring it backup ?

the easiest way is to make donations in a temple, but this can be costly.
Another way is to help people in some of the minor quests.
Have you stolen things and been caught or upset people or killed inocents. This may have set the guards off and might be hard to undo.
Rob