secure authentication and session management

hi!
I'd like to get your opinion on the security of my authentication and
session management scheme.
the user enters their username and password and i compare the hash of
both the username and password with values stored in an encrypted
file. if the comparison is successful i create the session. the
session is simply like what php does, a temp file with a random string
as its name. the file stored things like username, page accessed etc.
the string itself (filename) is stored as a cookie on the client side.
Each time the client accesses a page, i check if the cookie exists,
get the filename and see if such a file exists with. if not the user
is directed to the login page.
the cookie is timed so that it expires after 1hr.
the whole exchange takes place over SSL

any thoughts on the security of such a scheme and potential ways of breaking it.

thanks

cheers