Welcome to the Tableau Community. Where are you getting stuck while trying to map the postcodes to your data? If you could share an example of the data, we may be able to help directly as well.
Here is a KB related to this topic as well - http://kb.tableau.com/articles/issue/unable-to-create-uk-maps-using-postcodes
I have attached an example filled workbook built with Tableau 10.1.1
UK Postal Codes_Tab_10_1.twbx 47.4 KB