You will find that wood fires require a little "enhancing" at the time of shooting, to get adequate flaming. (adding some small kindling that will flame, some paper(which is brief), etc.)
On the other hand, a gas log can be adjusted to just the right effect, and it will maintain throughout the session.
It is also possible to use strobes behind colored gels, if the fireplace will go somewhat out of focus, and not even have a real fire.
In the case of a real fire, you need to drag the shutter to a shutter speed indicated by reading a grey card next to the fireplace, and illuminated by the fire, to balance with the strobes and f/stop in use for the flash exposure.
Don't forget to warm the strobes with gels to enhance the warmth of the light to be compatible with the fireplace environment. Dropping the color balance down to about 4800 degs. Kelvin should render a nice effect. [img]/ubbthreads/images/graemlins/smile.gif[/img]