Ciscotex is correct, but given your admitted "newbieness"
here are some step-by-step instructions:
1. Go to
Cisco Systems, Inc
2. Click the "Register" link at the top of the page
3. Complete the form as indicated (name, email, username, password) and then under "Register for Additional Access" check the box for "Service Contract Owner"
4. Click "Submit" and complete the next couple of pages of questions - don't worry, there's not much to it.
5. You'll then receive an email from Cisco with a link to activate your registration. Follow the link and...
6. ...you'll be prompted to enter your Service Contract Number, which will then allow you to access downloads specific to your product when you're logged in to Cisco.
7. Once logged in, under Support Links you'll see a Downloads link - click it
8. For the Product Category, click Cisco Secure Software
9. Now under Security Appliances, click Cisco PIX Security Appliance Software
10. Then click Download PIX Security Appliance Software
Or, once you've registered and added your contract, just go directly to the PIX sofware at this link (the end result of all the steps above):
http://www.cisco.com/cgi-bin/tablebuild.pl/pix