Okay... Gaara has never been in a real battle ever, because the sand demon/ kazekage protects him. Neji, on the other hand, has a practically impenetrable defense, is very fast, has byakugan, and the tenketsu hit thing. Even though the sand shield uses the kazekage's chakra, the armor, which i think is more effective, uses Gaar's chakra and can thus be shut down if his tenketsu's are closed. Also, the sand shield / desert coffin are slow moving and can be 'cut', as we see in some of the other battle's Gaara has been in in which he hasn't killed the other guy outright. I think that there would be no way for Gaara to win. Plus, the only reason Lee didn't completely kick his ass is that he opened five of the gates and messed himself up. Gaara didn't deal him any damage until that. And Neji is stronger than Lee anyway. So EAT THAT GAARA!!!!