It is not recommended to increase pixels via photoshop more than 200% the original.  Otherwise, you get a soft image not good for viewing. Photoshop will calculate the color of the additional pixels based on the surrounding pixels; this results in reduced jaggies but also no crisp lines.   Bryce defaults rendering at 72 ppi, but as Nazul said if you render to disk you will be given the option of dpi quaility and will show you the dimensions of the resulting image at that setting.