[svandamme]

check if the driver for the wifi card has seperate power saving options
turn em off

check if you can set the preamble on the wifi card, and on the router
set them all to long preamble only.


Check if you have an option to control roaming tendencies
If possible, set to the least setting : eg, the one that does not make the card look for possible other AP's, and stick to the one it has.


Is all your hardware 11N ? if so, set all your hardware to N only
If not , set all of it to G only and see if that helps