Developed In 2005, Need To Go Back To 2000

I've developed a web application and to be honest I've been a bit dumb and not checked with my hosts. I assumed they used SQL Server 2005. But no, they only use 2000.



I'm sure I'll come across more problems but the first I'm having is I've used the ROW_NUMBER() function in a few stored procedures, but in 2000 I'm getting this error message



'ROW_NUMBER' is not a recognized function name.



Here is the stored procedure for reference



SELECT RowNum
FROM
(
SELECT id, category, ROW_NUMBER() OVER(ORDER BY id) as RowNum FROM custrecords
)
as CustRecord