Planet "b"
The one planet so far discovered for 51 Pegasi is planted well within the tidal braking zone, far closer to its sun than Mercury is to ours. The planet has a minimum mass of slightly less than half that of Jupiter. We say "minimum" because we are uncertain of the planet's orbital inclination. If the orbit is exactly edge-on, then the mass equals this figure (0.468 M_J). If the orbit is highly inclined to our line of sight, then the actual mass is significantly greater than this.

New Earth?
The eco-zone is fully outside the tidal braking zone, making an Earth-like world possible from that standpoint. Such a world is also safe from any orbital interference this "red hot Jupiter" might otherwise cause. If more recent catalogs are correct in classifying 51 Pegasi as a sub-giant, then any world that was habitable would now be challenged by climate change generated by differences in the output of its sun. Website www.exoplanet.eu shows 51 Peg with a mass of 1.11 times that of Sol. If this is correct then the likely spectral type of the star when it was in main sequence is F9.5 V. This might mean that temperatures have dropped since the changes started. This might also mean that 51 Pegasi has not fully attained its status as a sub-giant, something that further research may clarify. If an Earth-like world exists in the 51 Pegasi system, it might be experiencing an Ice Age, or a great cooling compared to its prior climate. As this world's sun matures to full sub-giant status, the climate will likely swing in the other direction making such a world uninhabitably hot.