You may well be able to do this in Device Manager under the advanced tab , look for something like CAM ( constant awake mode , or similar under the power settings . Alternately , look in Win7's power settings in Control Panel , find you power plan and go into the advanced settings there , under networking ( or similar , don't have a 7 machine to hand at the moment ) and see if adjustments can be made from there .
I did make some changes in the power settings and in the advanced tab but did not find anything called CAM earlier... I will take a look and let you know what I find. I know you could make a change in XP that would work, but it has been so long since doing it I can not recall where the change was made.