If you have a desktop PC with something like
this in it (an internal card with an antenna sticking out the back of the computer), keep in mind that the metal case effectively shields it from one side and you may have to reposition the computer to improve the connection.
The most likely source of persistent interference would be cordless phones, if you have any in the house. Most of them operate in the same band.
My personal opinion is that WiFi was meant for laptops and other portable devices, not as an alternative to proper cabling for stationary computers. It will always add latency, drop a packet here and there, suffer from interference, and just won't be as reliable. You would be much better off running a cable -- it may be difficult, but usually isn't impossible.
