NI requires a free user account. If you don’t have one, create it. You do not need a service contract for legacy runtime engines—they are generally free to redistribute.
If the NI website redirects you to a subscription page, open a support ticket. Explain that you need Runtime Engine 7.1 for a legacy PXI controller or Windows XP system. NI support will often provide a direct FTP or HTTP link to the exact installer. labview runtime engine version 71 download high quality