Order numbers are automatically generated via the OrderNumbers table in the database. You would need to re-seed this to skip to using the next number you wanted. As an example, you might want to reseed like this
Code:
DBCC CHECKIDENT ('OrderNumbers', RESEED, 2013000001)
This would allow you to have 999,999 orders for the year 2013. But you would have to reseed every year on the 1st Jan @ 00:00:00. Also, you would run out of order numbers in the year 2147 after the 483,647th order of that year!
Hopefully I won't be around then to take any flack when it all goes wrong
Google 'sql server reseed', 'sql server identity' and 'sql server int column max value' for more info.