You can use the Windows Vista Task Scheduler to make your computer wake from sleep automatically at a pre-set time. To do so, click Start Menu > All Programs > Accessories > System Tools > Task Scheduler.
In the RHS Panel, select Create Task. A new window will open. Here under the General tab, fill in the Name and Description. Also check, Run with highest privileges.
Under the Triggers tab, click New. Another window will open. here. Select One time (or Daily if you want it repeated every day at a particular time). Set the Date and Time when you want your Vista to wake up from Sleep.
Next under the Actions tab, you have to mention a task. Click New. You can run a simple task, like say, first launching & then closing the command prompt window. This thus will wake your Vista machine at the pre-set time to carry out the task !
Select Action as : Start a program. To schedule a task that executes the command cmd.exe with command line arguments, copy-paste under Program/script
Under Conditions tab, check on the Wake the computer to run this task check-box. This is important!
Click OK and Exit Task Scheduler. Your computer will wake up from Sleep at the particular time ! Thanks on10.