INSERTS with MS SQL Server columns with newid() default values

My first steps in RoR .. and it turns into a bad dream when it come to SQL Server!

I have this table 'Tbl_People', with 2 fields

id_People primary key, automatically generated by SQL Server with newid() default value, namePeople is a string

I have an ODBC connection to the database. I can list the records, but ... I cannot make any inserts in the table. The INSERT string generated by Ruby is the following:

INSERT INTO Tbl_People (id_People, namePeople) VALUES('newid', 'GRONDIER, Evelyne')

And will be refused because the string 'newid' cannot be inserted in the uniqueindentifier/primary key field 'id_People'.

The error returned is: 'DBI::DatabaseError: 37000 (8169) [Microsoft] [ODBC SQL Server Driver][SQL Server]Conversion failed when converting from a character string to uniqueidentifier'

It seems to be so obviously a big and basic problem that I feel I missed something usually written in bold on each RoR training document such as 'Don't try INSERTs through RoR','uniqueIdentifier is Chinese to RoR', or 'RoR doesn't work with MS SQL Server'...

Any idea?