18 December 2008
If it is central excise invoice, then it should only be in Indian Rupees. Ref: http://www.cbec.gov.in/excise/cx-manual/manual/chap4_part1.htm#ch4_p1_1
22 December 2008
It depends upon the terms of contract. As payment for all contracts with local parties are to be made in indian currency, there is no reason that the bill should be raised in another currency.