For the minimum required IOS version for IS-IS features please refer to:
http://www.cisco.com/univercd/cc/td/doc/product/software/
ios123/123cgcr/ipv6_c/ftipv6s.htm#wp10 04964
Before configuring the router to run IPv6 IS-IS, globally enable IPv6 using the ipv6 unicast-routing global configuration command.