Select data from list box and automatically display data to another text box

Hi,
Im new in asp.net (in programming actually  )
I really need your help to solve my problem. I have create a form, what i need is once user click on Supplier name in the list box, in text box for supplier address, phone number and fax will automatically appear (extract from the same table with supplier name).
table : tbl_SupplierDirectory
Field: CompName (for Supplier Name and the id : supName)
        CompAddress (for Supplier Address and the id : sup_add)
        CompPhone  (for Phone Number and the id : phone)
        CompFax (for fax and the id : fax)

I really appreciate your help..thank you