The SB Live! is still a hardware sound card. Sure, it doesn't support EAX 4.0, and it's limited to 4 channels, but it's still not bad, and it's hardware accelerated.
The AC'97 on a non-MCP-T board, which the NF7 isn't, is a) fully software controlled, i.e. your CPU has to run the sound hardware as well as figuring out where the guy's head you just blew off in Unreal Tourney will go and b) is run through the (((WORST)))(((DAC)))(((EVAR))) that is the Realtek ALC650.
Basically, AC'97 means 3d sound will inflict a sizeable CPU utilization hit on you, and the ALC650 is a lousy fidelity sound chip, even when coupled with a stronger DSP, such as the one built into the MCP-T southbridge.
I'd use the Live!.