You need to escape the backslash with another backslash. From d:\nibble.csv
to d:\\nibble.csv
Do this way..
<?php
$sql="BULK
INSERT nibble
FROM 'd:\\nibble.csv'
WITH
(
FIELDTERMINATOR = ',',
ROWTERMINATOR = '\n',
FIRSTROW=2
)
";
mssql_query($sql);