I'm not sure how well they would work on older (specifically not copper or corroded) wiring, but I would imagine any power line that isn't a safety hazard would probably work fairly well.

I'm not sure how much those adapters run, but the other option is that you simply get a good wireless router and make sure you have a good wireless adapter on your computer as well. There are a lot of cheap routers around and they have issues, from poor signals to signals that look good but are slow or drop out occasionally.
I fairly recently bought a new router and it has fixed all of the problems I was having with my previous ones. I've pretty much given up on Netgear and Belkin wireless products, routers especially. I know the router is Asus, I'm not sure about the wireless adapter, but I think it might be Asus as well.