From the Boot Camp license agreement:
So, your Boot Camp beta either expires when they release the commercial version or on September 30th, 2007. By that time Leopard will already be released and it will be built-in.
Term of License. The term of this License shall commence upon your installation or use of the Apple Software and will terminate automatically without notice from Apple upon the next commercial release of the Apple Software, or September 30, 2007, whichever occurs first.
So, your Boot Camp beta either expires when they release the commercial version or on September 30th, 2007. By that time Leopard will already be released and it will be built-in.