SIP system for free?

Hi. I am still new to networking(don't worry, i'm taking the networking class )
So anyway, I want to set up a SIP system. Here's what I have:

1. Broadband Internet
2. Optimum Voice VoIP
3. Windows Server 2003 machine
4. Windows XP (always on)
5. A couple of softphones
6. NO money

So, I would like to make it so that when you call the line, it goes to the recorded message, wherein you can select different selections, 1 which will go to the line's phone directly, and about 6 that will be forward to other lines.