FCC limits for new 802.11a standard are different for 3 bands, as follows:
5.150-5.250GHz Indoor 50mW (17dBm)
5.250-5.350GHz Indoor/Outdoor 250 mW (24dBm)
5.725-5.825GHz Outdoor 1 W (30dBm)
An article in WNN WiFi Net News says this:
In the 2.4 GHz band and parts of 5 GHz, the maximum power from the radio is 1 watt (W), and the effective power (EIRP) is 4 W on an omnidirectional antenna. (You can push far more power if you narrow the antennas beam. And parts of the 5 GHz band restrict radio power below 1 W.