insert into vs. select into

can somebody tell me the difference between select into and insert into statements in sql server.

for example: How
SELECT LastName,FirstName INTO Student_bk FROM Student

is different from

INSERT INTO Student_bk(LastName,FirstName) Select (LastName,FirstName) from Student

Thanks.

Try running them on a non existent destination table ....

Thanks for the reply, the confusion i m facing is, in my stored procedure If I have

set @strSql1='SELECT field1 INTO #GetHours from tbl_Hours' +
' WHERE num_Record =' + CONVERT(varchar,@f2)

EXEC (@strSql1)
WHILE (SELECT COUNT(*) FROM #GetHours)>0
BEGIN
...
...
END

it gives me an error in Select cout(*) statement, saying "invalid object #GetHours"

However, if I change the SQL statement to this,
set @strSql1='INSERT INTO #GetHours(field1) ' +
' SELECT field1 FROM tbl_Hours' +
' WHERE ....'

it works. The "Select into" statement also works if I don't build a dynanmic string. However, I must build a dynamic string as I still need to add few more "and" clauses depending on the business logic.