Sometimes, unfortunately, wireless internet can let you down. Particularly in older buildings with thick walls, you can occasionally find that a signal just cannot be received from the access point. Wireless N technology is a leap forward but even then, depending on the layout of your building, it might be the case that wireless it not a suitable solution.
There is a solution however. Devices are becoming increasingly available that allow you to run ethernet over power cables. You'll need at least two and you plug one into the mains near the router (and then connect with a CAT5 cable) and then you plug another one into the mains in the room in which you want access, and connect up to your computer with a cable.
It's an almost instant setup and works a treat in giving you network access in hard to reach areas. Different speeds are available, and the more you pay the faster the LAN speed you will get.
The Devolo 1154 Homeplug High Speed Starter set offers speeds of 85Mbps and costs £94.99 from PC World.