Best way to Make Windows XP or Windows 7 Wakeup at Backup Time?

I have standalone windows xp Machines that are in standby during the night and standalone windows 7 machines that are in sleep during the night. I am wondering what is the best way to get them to wake up so that my backup program can run a scheduled backup job at like 2am?

I have tried just setting the scheduled backup in my program (Cobain Backup), but it doesn't seem to work very often, and I think that the machines are just not waking up. Is there some sort of scheduled task that I can create or something in XP or 7 to make it wake up at a certain time automatically?