You can buy aerials to improve the wifi signal reception. These are usually only feasible for the access point (and even then not all APs have replacable aerials) or desktop wifi cards, with SMA connectors.
Given that the standard PC wifi card will have the aerial at the back of the PC, with a ruddy great lump of tin on top of it, probably a monitor in close attendance also, adding an external aerial is probably the single best thing you can do.
I bought a very simple antenna that sits on the top of the PC case (magnetic base) from Maplin for £10 - here's the
link. Makes a huge difference!
SD