extending a wifi network

[isocrazy]

Hey. i have a microsoft wireless B base station. and i have a notebook with centrino. i get a decent signal 4/5 bars or 3/5 bars and my speed fluxuates from 11mbps to 1 or 2 sometimes 5.5. i was curious to k now a way i can strengthen the signal with an access point or somebody can direct me to which one would be the best and the cheapest if possible. anyways thx in advance

or even if there is a way to build a simple antannea to strengthen the signal would do fine. instructions pls