How do i use multi currency in sales order form

Hi Evan, 

Thanks for the reply we have multiple customers in our salesorder form, recently we had one Indian customer so we need to add INR to the saleorder so as it shows up INR insted of $. 

Note the same sales order contains $ as most of our customers are in USA.

Hope i am clear, please suggest best method of doing.

Thanks once again
Raghu