Standby and sleep are the same thing. Are you talking about that you want it to Hybernate instead of Standby? What is the issue exactly? You want it to standby after 20 mins and it does not, or it does and you want it to stop?
Some default XP power manager settings may not work properly if you don't have the vendor extentions installed. Downlaod the Thinkpad drivers for your model, it should have Power Management drivers available. See if that fixes whateve rissue you are having. BIOS update also can fix things.