Need to find a solution to my range problem

While it may seem that this would be better placed in wireless networking, I felt it would be best here.

I have a fairly large house, and I have an oldish computer, which has a D-Link Wireless G adapter. It works about 75% of the time, though at low speeds. It is, to say the least, unreliable. I can run some games and when I go to play them over the internet, I often disconnect. I believe this is because of the range, as I have moved the computer closer and experienced faster speeds, as well as using differnet adapters, and I have the same problem. I know that it is not the internet, as I have a gaming computer plugged directly into the router and it runs fine.

I am building a new gaming computer and I feel that this will be a major issue as I try to game. It was never a major issue before, as I mainly only used it to browse the internet (as well as the casual game, as mentioned above).

I cannot move the computer out of the room, and my entire house is finished (with the exception of one room across the hall from mine. I do not have ceiling tiles, and therefore feel wiring ethernet would be a major hassle, as well as costing a lot of money getting an electrician to do it (although I am not sure about the costs of wiring ethernet, I could not get any good quotes over the internet).

Wireless-N seems expensive, but I am willing to spend the money if it will work. How much more efficient is wireless-N?

Also, I have looked at Ethernet over Power, although I am not sure if it will work in my house. I have two breaker boxes, and I therefore assume that there might be some problems with the connection.

So, here I am, asking for help.