Use a function in update query

I have a table called isbnCodesTbl, in my Access 2003 database (see below).  Data is regularily imported into my webproducts table.  Webproducts has a field called isbn with a numberical value for each product. The isbn code corresponds to the isbn field in isbnCodesTbl.  I want a query to update a 2nd webproducts field called ExtText3 with the description that corresponds to the isbn code.

EG: update exttext3 with ConvertFunc([isbn])

isbn      desc
0      available, displayed
12      Duplicate SKU, not displayed
11      Has a New SKU#, not displayed
9      No longer in Inventory, not displayed
6      Out of Stock, can by reserved, display
8      Out of Stock, not displayed
7      Phone Order Only, displayed
10      Seasonal, not displayed
13      Sold by client's organization, displayed
1      Waiting for Instructions, not displayed
2      Waiting for Picture, not displayed
4      Waiting for Size, not displayed
5      Waiting for SKU, not displayed
3      Waiting for Text, not displayed
14      Waiting for Web Page, not displayed
15      Requested off website, not displayed

Thanks for any suggestions.

David