Recently, I've been setting up my HTPC / Personal PC to automatically go into s3 sleep in Windows Vista. This sleep mode allows the computer to nearly shut down while still being able to wake back up nearly instantly and bringing you right back to where you were.
However, as many Vista users have experienced, when you come back from s3 sleep you may not be able to reconnect to the internet. For some reason, s3 sleep can kill your NIC card until you restart or until you disable and then enable it in Device Manager. I was having this problem and it was quite annoying since I need to have my PC on at all times to record shows in VMC.
This is a quick little post to share what fixed this problem for me. If you need help setting up s3 sleep in Vista and/or getting it to work with Media Center, let me know.
First, navigate to your device manager (Right click "Computer" and select properties. Then select "Device Manager" in the top left). You will see this screen.

Click the "+" next to your "Network Adapters". Now double click the NIC that you use for internet. (If you have multiple and you don't know which you use, select the first one in the list). Another window will pop up which looks like this:

Now click on the "Advanced" tab at the top and scroll the list down to the bottom. There should be an entry that says something along the line of "WakeOnLAN From Poweroff". Select this option and then make sure it is
enabled.

Now navigate over to the "Power Management" tab on the far right. Now check the box that says, "Allow the computer to turn off this device to save power".

This will allow the computer to shut off the NIC and power it back up so it does not get hung up in purgatory, thus allowing your computer to have internet when it wakes up from S3 sleep. Personally, I do not let the NIC wake my computer from sleep, as it is very sporadic and I currently have no use for it as I can still record when it is asleep and it will go back to sleep when it is done.
That's it! I hope this helped you.
Mr. Lemons