Mitch, as thorne pointed out, the taskbar is "drag and drop". This means you can put it either in the top of the screen, the right or left side or the bottom.

What has happened is that you accidentally (or windows arbitrarily acted) put the task bar on the right side of the screen and locked it in place. As he stated, you merely have to right click the task bar, uncheck the "lock task bar" option and then left click, hold and drag. It's that simple.