How do I track two sites at the same time?

My merchant is letting put Analytics code on their success page to track goals, but I’m sending traffic from two sites, one organic and one ppc. Analytics has different code for each site. Will it screw up anything with my stats if I give the merchant the code from both sites to be put on the same success page?
I found this link about multiple sites in Analytics help, but I’m not sure if it applies to my situation:
http://www.google.com/support/analytics/bin/answer.py?answer=55503
Thank you.

See original post by Garp