The Start bar in WinXP, and most later Win versions, can be "moved off" the page, just by clicking and dragging it down. If you hover your mouse pointer on the edge of the screen, click and drag toward the center of the screen, it should bring the bar back into view.

Once you get the bar back, right clicking on a blank space on the bar should give you a choice to "Lock Toolbar" and if you click there it will put a check mark on the choice and the toolbar should stay up. With the "lock" on, you shouldn't be able to drag the toolbar off screen.

If the bar has just been moved off, it can be a little tricky to find exactly where on the edge of the screen to click to drag it back up, so giving it a few tries may be necessary before you give up. Pressing the "Windows" key (usually between Ctl and Alt on the keyboard) should bring up the Start menu, so you can get to programs and settings until you find the toolbar if you have trouble.

John