License key Question

Question:

Can I install SFHA 5.1 SP2 for WIndows using SFHA 6.0 for WIndows' S licencse key??

Since Customer's OS is WIndows 2003 Server, So we can only install SFHA5.1 SP2.

SFHA 6.0 is not support WIndows 2003 server.

Thanks~