HELP? HTTP HEADER GURUS etc?

Hello, Not sure if this is exactly focused on PHP, but i thought some of you guys might know. The general problem: I want to be able to send SMS messages from my computer using one of the free SMS services. I want to be able to do this without logging on each time - i.e. from a program (eiither C or java or the like). In essence, the problem is to get a program to 'Log In' to a site, and keep the user 'Logged In' (by sending cookies with each request i presume..) So the 2 questions are: 1. how do i send a POST query (containing login details) to a page? (if it were GET, i could just append to the URL, how do i do it with POST?) 2. once i have sent this (correct) login, i will receive back a cookie. I can store this, but need to know how to send it back with each request? (in the header somehow i presume..?) Thanks in advance, Jonathan