This standby icon is when you click shutdown?? Also, if you press Shift it turns into Hibernate Icon. However, these are only enabled if you have enabled APM (some old motherboards dont use it) and also enabled XP to enter standy mode or Hibernate mode.

Usually after a clean install of XP, you need to run the Motherboard Chipset driver CD, which loads all appropiate drivers for AGP, PCI, USB etc etc This tells XP of any powersaving features the MB may have.

By the sounds of it, you may have missed this last step - actually I missed it last nite on new install lol - but once you installed the drivers all is good