I can't explain it's location but the "What is it" part is here, This is a copy and paste from the "Help and Support" section of XP. If you type quick launch into the search section of the XP "Help and Support" section, you will get a lot of information about it.

Quick Launch
A customizable toolbar that lets you display the Windows desktop or start a program (for example, Internet Explorer) with a single click. You can add buttons to start your favorite programs from the Quick Launch location on the taskbar.