Vista goes to sleep while I'm using its network share

Hi,

I have a Vista machine that I have configured several R/W network shares,
and it is also configured to go to sleep (S3) after 10 minutes of inactivity.

While I am using the network shares from across the network, the Vista
machine apparently thinks that it is idle and it goes to sleep after 10
minutes, even if I am reading or writing the shares at that very moment! Is
there a way to make the Vista machine stay awake while I'm using its shares??

I have tried setting "Media Sharing" to true, but when I do that, the
machine just plain old never goes to sleep at all, even when it is truly idle.

Thanks
Aaron