How to handle TradeInn?

[sniffing]

Hi there,

Can some one please share there experience on how they are handling TradeInn.

When producing the Purchase Order, is there any way that the Amount of the Trade-In can be entered (Credit amount) against the amount for the New Asset?
i.e. Purchase Order

New Car 35,000
Trade-In (15,000)
-------
Balance 20,000
-------
Any help on this would be really appretiated.

Thanks,
Kiran