Open the textbox properties for the field you want to have the link:

And select the Navigation tab:

Open the Jump to URL expression builder and insert the following expression:

="javascript:void(window.open('http://maps.google.co.uk/maps?q=" & Fields!PostalCode.Value & "','_blank','scrollbars=auto, resizable=yes, status=no'))"

 

This will open google maps in a new IE window using the results of the field as the search criteria

 

Click here for more info on the javascript open method

 

Or alternatively you can use the expression without the javascript to open in the current IE

 

="http://maps.google.co.uk/maps?q=" & Fields!PostalCode.Value

 

This is just one application of the Jump to URL functionality, this can be used in many ways, e.g. Linking to customer or supplier websites (providing you have the website address as a field in reports dataset)