Hi rocky,
Please consult the following MSDN articles and link to see what would work best for your environment and infrastructure:
http://msdn.microsoft.com/en-us/library/aa475435.aspx
http://msdn.microsoft.com/en-us/library/aa558765%28BTS.20%29.aspx
http://stackoverflow.com/questions/1951469/network-load-balancing-biztalk-instances
Hope these resources help,
Daniel.