Most US Wireless adapters are nerfed due to FCC regs, search around for 350ma adapter, Cisco does them. Check out if your wireless access point has international firmware options as well, these might run it at high output levels.
Check out internal omnidirectional antennaes, might help too.
BTW, you do realize wireless networks are for the most part totally unsecure (unless you use something like a Sonicwall TZW).