Assigning values of a Lookup Table in to a Main Table.

Hi Experts

My requirement: I need to update value of Lookup Table into a field of Main table. Once user selects data in Main Table, based on selection (from Lookup), i want a value to get updated in another field of Main Table.

Example: Category_Table (Lookup Table) - Has filed's - cat-Name and Cat-Type. In Main Table, On selection of Category, I want to populate value of cat-Type into Main Table.

Regards