Do you have your own Wifi Router or are you using a community wireless? It sounds like you are in a place where there are many wifi networks. This can make the 2.4Ghz band miserable. If you have your own router I would seriously consider upgrading so you can use 5Ghz channels. There is much less interference on that band.
Well, if you're getting a lot of interference through wireless and you really can't lay cable you could try a few things:
1. Try different channels. The ones to use are 1, 6 and 11. The rest just overlap
2. Try a different wireless card. Some routers work better with the same brand of wireless card or USB adapter
3. Get a more powerful, dual band router. 5Ghz tends to be a lot less cluttered and so will have less interference. If your walls have metal in them though or are very thick 5Ghz can be more susceptible to this.
4. Get Powerline. These connect using your standard electrical sockets and are usually better than wireless for stability or latency. It's essentially a wired solution without having to lay cables.