For a login application, how would i go about checking the sha1 value of a password?

Question

How would i go about adding a function that checks the db for the users sha1 password value?

Answer 1

In PHP there is a sha1() function already. So it's as simple as calling this function:
if (sha1($userInput) == $yourStoredPassword) // The password is correct
But remember that sha1 without any salt is not a very secure hashing solution.