Vista Taskbar Problem

I have Vista Home Premium 32 . Originally active windows would be in the middle area of the taskbar . At some stage this has changed to 2 ( maximum) small squares to the left of the notification area , and a little thing with down/up arrows . If there are more than 2 active windows , I can use the arrows to scroll up down through the small squares . Can't find how to reset this .
Thanks .

There is a dividing bar between the areas.
Unlock the task bar, if it is locked.
Point to the dividing bar, click and hold while sliding it in the direction you want.

Thanks ua549 - that was it . It appears that the both dividers had somehow turned into this one arrow up/down/scroll thing .