With great difficulty.
The only solutions here would involve adding extra hardware to the pub, in the form of either repeaters, boosters or a wider gain router. None of which the pub is likely to agree to readily. Nothing you buy is going to solve anything, unless you move closer to the pub.
If your intention is to get effectively free internet on the back of what I presume is a public wi-fi point in your own home then your best bet is to consider having the internet installed at home.
Edited by Neil Jones, 23 November 2010 - 04:44 PM.