Is there an easy way to have Vista exit from sleep mode at a given time?

I have an alarm app that goes off in the morning, and at the moment i just have to leave my computer all the way on, with the screen off, because if it’s in sleep mode.. the alarm will still activate, but Vista automatically shuts off the computer sound, when it’s in sleep mode. So I’d like something that could either 1) Have Vista exit sleep mode at a given time, or 2) Change the settings of sleep mode so that the sound is no longer muted. I’ve tried both but to no avail.. any suggestions?