[b]I have double glazing throughout and know 1 has blown and needs replacing but can you also get condensation ( only very slight) inside of room window when you have dble glazing? or do they all need replacing?[/b]
If you mean condensation is forming on the inner surface of the glass (nearest the room) then this is normal.
Its a myth that double glazing is the cure for condensation on windows, in some cases it can even get worse. Condensation will happen where warm air meets a cold surface, which as this time of year is most windows, even double, or triple glazed ones.
If you mean condensation between the panes of glass, then the seal has blown and the unit would need replacing.