wireless 802.11b fcc regs?

does anyone know the fcc regs for broadcasting using 802.11a/b? if you're using the unlicensed spectrum (2.4 GHz) for xmit, do you need an fcc permit to use the spectrum beyond a certain range? I visited a company (www.luxul.net) and purchased a point to multipoint antenna system capable of xmitting 512Kbps-11MBps up to 15 mile range (they have an unusual 45 degree directional antenna system -- works great.) anyway, thinking of launching a free encrypted wireless data service in washington dc area, but unsure of fcc regs regarding the use of 2.4GHz spectrum (don't expect free = super robust.) also, am in need of two antenna points...would appreciate suggestions other than the north clock tower at georgetown univ. phillip