Numbers Less Than Zero

In a pretty standard select statement (as shown), i want to return 0 when "dbo.v_AgentOrderTotals.Total - dbo.v_AgentAmmountPaid.total - dbo.v_AgentCommClean.total AS amount_outstanding_commission" is less than 0.

SELECT     dbo.t_Agents.agent_code, dbo.v_CurrentParamPaymentTotal.ammount AS weekley_payment_total,
                      dbo.v_AgentNumberOfCustomers.count AS number_of_cust, dbo.v_AgentAmmountPaid.total AS total_paid,
                      dbo.v_AgentOrderTotals.Total AS ytd_order_total, dbo.v_AgentOrderTotals.Total - dbo.v_AgentAmmountPaid.total AS amount_outstanding,
                      ISNULL(dbo.v_AgentAmmountPaid.total / dbo.v_AgentOrderTotals.Total, 0) * 100 AS ytd_percentage,
                      dbo.v_AgentOrderTotals.Total - dbo.v_AgentAmmountPaid.total - dbo.v_AgentCommClean.total AS amount_outstanding_commission,
                      ISNULL(dbo.v_AgentOrderChange.amount, 0) AS net_weekly_order
FROM         dbo.t_Agents LEFT OUTER JOIN
                      dbo.v_AgentOrderChange ON dbo.t_Agents.AGENT_ID = dbo.v_AgentOrderChange.AGENT_ID LEFT OUTER JOIN
                      dbo.v_AgentCommClean ON dbo.t_Agents.AGENT_ID = dbo.v_AgentCommClean.AGENT_ID LEFT OUTER JOIN
                      dbo.v_AgentNumberOfCustomers ON dbo.t_Agents.AGENT_ID = dbo.v_AgentNumberOfCustomers.AGENT_ID LEFT OUTER JOIN
                      dbo.v_AgentOrderTotals ON dbo.t_Agents.AGENT_ID = dbo.v_AgentOrderTotals.AGENT_ID LEFT OUTER JOIN
                      dbo.v_AgentAmmountPaid ON dbo.t_Agents.AGENT_ID = dbo.v_AgentAmmountPaid.AGENT_ID LEFT OUTER JOIN
                      dbo.v_CurrentParamPaymentTotal ON dbo.t_Agents.AGENT_ID = dbo.v_CurrentParamPaymentTotal.AGENT_ID

 

Any ideas how i do this?

Cheers
Anthony Swift