Those powerline devices should be banned! I suspect that if the RSGB gets OFCOM to do its job, they will be. As said, they will only work if both ends are on the same phase, and then only over a limited distance. Meanwhile, they are transmitting on frequencies for which they are not authorised, and causing interference to the services that are authorised for those frequencies.
I've developed a simple rule of thumb that says a typical 802.11g wireless router has a range of 50 feet, three normal internal walls, two brick walls, or any permutation thereof. I think a Cat5 cable heading towards your house to as close as it can get, with a wireless access point on the end of it, is the way to go. If the Cat 5 will reach all the way, so much the better.
With wireless, it is (as said above) important to "sniff" the spectrum and pick a channel away from others in the neighbourhood. Then see if it works - if not, there may be a cordless phone around, in which case try another channel.