Having to position WordPress widgets in different places on different pages on the same sidebar can be tricky. The most common solution is to use the WordPress Widget Logic plugin. Combined with Conditional Tags can be a powerful tool when delivering widgets. However it can very quickly become complex. Administrators with little technical knowledge can also find this solution daunting.
An alternative to Widget Logic is a plugin called Widget Block. Widget Block works in a very similar way to Widget Logic, but is much easier for clients to use. It works by appending a textarea to the base of your widget forms where you can enter the URLs of the pages and posts you want the widget to appear on.