how do i change my system tray in windows xp to a horizontal position?
You can move the entire task bar (start button, task bar, systray).
Horizontal means going across, so that is where it normally is. If you want to change it to vertical, on either side of the screen:
Right click empty area of taskbar.
Click Unlock taskbar.
Point to end of taskbar, grab a handle, and drag to where you want it.
When finished, go back to properties & lock taskbar.