sorry it took so long to reply, since not many people actually frequent this group I made I don't check it regularly, and I never got the Email for when you posted.
Unfortunately, I have yet to find anywhere in BIOS you can program it to come on. I have a Old 2003 model Dell with this same option, and it comes in pretty handy. What I have learned from that system is you can schedule a task in Windows 7 Schedule Manager to wait til current tasks finish, then completely shut down the system. I set my Dell to startup at noon, and shutdown at Midnight, so effectively is running during the peak hours people would use it. But, since you are telling it to sleep, you may be able to let it sleep when not in use, and setup a Wake timer in Windows.