How to Automate Invoice Based ON LST/CST/PAN

Hi Friends,

Current Client Have a requirement whenever customer has a

1.LST/CST/PAN no. they have to print TaxInvoice and No. Range Should Be different

2.If Customer Doesn't have Tax Details (LST/CST/Pan) it should be Print Retail Invoice and No. range Should Be Different.

How to Make it automate in the Noraml proceess

Ex.

VA01-VL01n - Tax-Invoice

                     - Retail Invoice