did you know that the P1900 has a deadman timer that can cut the power to your mac after 72h of sleep? That way your battery will definately not be drained. If you want to use that, I suggest you use http://www.jinx.de/SmartSleep.html
Anyway, back to your question: You could create an AppleScript to do the job.
This thread is not exactly on topic, but I suppose it will give you enough information to solve the remaining problem :-)