XP - OPK, microsoft partner program and activation

[atlantis]

Hi! I am building my first new PC using the instructions on this site and I found the step by step instructions extremely helpful. I have bought Windows XP Professional with SP2 OEM System Builder Pack to install on the PC. On the package envelope, there are instructions about installing the OS using the OEM Preinstallation Kit (OPK). I don't think the OPK comes in the 1 CD within the package. Anyway, I just put the CD into my DVD/CD drive and it installs XP onto my new hard disk. After installing the OS, the OS prompts me about activation. I went to Microsoft's web site and it mention something about enrolling in the Microsoft Partner Program. I don't want to enroll in the program unless absolutely needed. So my questions are as follows:
- Do I actually have to use the OPK to install the OS?
- How do I get the activation code for my new PC?

Thanks in advance for any advice.
Regards.