What has this got to do with ASP.NET? SQL would suffice.
INSERT INTO [Table2]( NRD)
SELECT MAX(NRRENDOR)
FROM Table1
' WITH (ROWLOCK, XLOCK, HOLDLOCK)
The correct way to do it will be to use @SCOPE_IDENTITY after you perform insertion as Tanner suggested. It will be worth noting that there is another way to get the current identity, ie, IDENT_CURRENT. You can use it like this
SELECT IDENT_CURRENT('Table1') + 1 as Current_Identity
Please note this too
Be cautious about using IDENT_CURRENT to predict the next generated
identity value. The actual generated value may be different from
IDENT_CURRENT plus IDENT_INCR because of insertions performed by other
sessions.
This comment from marc_s sums it all. How to get the next identity value from SQL Server