Differences between IOS and NXOS.

http://docwiki.cisco.com/wiki/Cisco_NX-OS/IOS_Software_Default_Configuration_Differences

IOS to NXOS migration tool
http://tools.cisco.com/nxmt/

Minimum Recommended Code Levels.
http://www.cisco.com/en/US/docs/switches/datacenter/sw/nx-os/recommended_releases/recommended_nx-os_releases.html

Data Center switching support forums on Cisco.com.
https://supportforums.cisco.com/community/netpro/data-center/server-network