Lee,
If the originator of the purchase order is always the one assigned to it, then you could just refer to the record owner field.
If you want to have the option of assigning someone else then you could set the default �assigned to� person within the button used to create the purchase order. Within a formula URL field you can dictate values of any fields that you want. Look at the formula for a bottom created in a parent record when a relationship is created as an example. All of those buttons set the �related � to the value of the record ID# of the parent record.
Just add an additional �&_fid_=� & URLEncode([current user email address]) into the formula.
