Susan:

Try:
AND(
{Order Complete?} =FALSE(),
{Doc Type} ="O",
{OELine Qty Backordered} >0,
OR(
{Cust #} ="TD5775",
{OEHead Salesperson} ="KINGSN"
)
)

The first 3 lines have to be true and only line 4 or line 5 need to be true.