my neighbour and i live +-50metres apart from each other, i purchased two 300mbps wireless usb wi fi network cards to help connect to each other, i have recieved these adapters as yet therefore i would like to know will it be possible for us to LAN a pc game such as UT3 without any hassles and on estimate what network speed will we experience?
Everything depends on the strength of the signal and all of the obstacles and interference (walls/floors/other barriers) between the two PCs and the router. If you can both connect and have decent signals, it should work fine, but there's no real way to even estimate without knowing what's between the PCs.
If you run into issues with signal strength, though, you can always buy a wireless access point and put it between the PCs. There are even models specifically designed for outdoor use.