Without knowing what we are dealing with (desktop, laptop, etc.,) it is difficult to propose a possible solution. That is why we frequently ask members to fill out their system specs in their forum profile area Link Removed
Depending on how old your computer and installed hardware is, it's possible that the installed drivers for your network adapter(s) is less than optimal for Windows 7 and its' power management APIs, make sure your driver version and date are the latest available from the device manufacturer's website.
IF you are talking about a wireless adapter you may want to check the Advanced Power Settings Options regarding your wireless adapter maybe set it to Maximum Performance. If it's a USB adapter you may want to...