Using Lookup Column Value in a Calculated Column

Hi,

I am using SharePoint Foundation 2010 and do not have SharePoint Designer installed.

I have a lookup column based on another list's description and I would like to use this additional column's value in a calculated column.

However I'm not sure how to reference the additional column in the calculated field's formula builder and it doesn't appear in the 'insert column' list.

Hope someone here can assist me.

Thanks!