Check the advanced and power saver tabs for your network connection in Windows Device Manager. (The quickest way to reach device manager is to run devmgmt.msc from the Windows search programs and files box you get when you cllick on the "Windows" icon. I can't remember if this was an icon or something more in Vista. I am using Windows 7 now.)
Look for any "Wake on" options and disable them. That will likely take care of the wake ups you are experiencing.
I hope this helps.
Thank you Mark! There was a 'Wake on' option which I disabled.