Prevent Windows sleep mode while downloading?

Does anybody have a way for Miro to keep the computer from going into sleep / hibernate mode while there are downloads active? I'm running Vista and have it set up to sleep after 30 minutes of inactivity. This is normally the desired behavior, but the system doesn't seem to agree with me that downloads should be considered activity.

So maybe this could be added as a Miro feature. Or, if someone is adept with the task scheduler and knows how to keep it awake and downloading for a certain time every day, that would work as well.