i dunno if this is the true answer, but i think i'll take a stab at this one.
on my T40, there's a setting to adjust the power save setting on my Centrino wireless adapter. if i look at the high power save setting, it says that i'll have best power savings. if i choose low power setting, then i get best network coverage.
so, I THINK in a nutshell:
high power saving = decreased network performance
low power saving = best network performance
or perhaps someone else more knowledgable can answer... just taking a guess here...
ok, if you look in your system tray, there should be a small icon with 3 lines, in the shape of a step going up. if you hover over it w/ your mouse, it'll say intel pro wireless lan xxxxx.
click on this and then a menu pops up. one of the options is "power save mode" and it'll open to the right where you can change the power options.