Dependant IDENTITY Columns

Anyone know if MS-SQL Server supports IDENTITY columns that are incremented for each new value of the column it depends on.

For exameple:
Let's say I have a client table with a ClientID column as it's PRIMARY KEY.
This column can be an auto-incrementing IDENTITY column.

Then I have an orders table. The PRIMARY KEY for the orders table is composed of (ClientID, OrderID). I would like the OrderID to be an IDENTITY field that increments by an arbitrary value (1 in this case) for every new value of ClientID...therefore creating a unique PRIMARY KEY.

The contents of the table would look like this

ClientID OrderID
------- -------
1 0
1 1
2 0
1 2
2 1
2 2
1 3

and so on....

MySQL (and maybe other RDMS's...I haven't checked) seems to do this automatically when you set a column as AUTOINCREMENT and then define a composite PRIMARY KEY on two fields.
I know this can be done manually using triggers, but I was wondering if there was a better way...

Thanks in advance