ms outlook change the from email sent from using vba code

have my out look that i use to send out a 20 -30 emails for work, and when it arrives it says from peter@abc.com , but need to say that the email comes from john@abc.com
i am composing the email out of a DB and building it in the back end as below but cannot see how to change the email from in the header even though  i have the other email set up in the email account, were is the default setting to set this up
any help would be appreciated
using outlook 2003


               Dim olapp As Outlook.Application
               Dim objmail As Outlook.MailItem
               Dim pos As Integer
               Set olapp = Outlook.Application
               Set objmail = olapp.CreateItem(olMailItem)
               objmail.BodyFormat = olFormatRichText