How do you plan to set up the two sites? Two domains, one domain with a subdomain? Or can one just be in a subdirectory?
I'm still thinking of solutions, but it would be good to know which options you could use.
1. http://www.domain1.com & http://www.domain2.com
2. http://www.domain1.com & site2.domain1.com
3. http://www.domain1.com & http://www.domain1.com/site2