Can you help me with iPhone syncing issues?

I am trying to figure out for a friend with an iPhone (3G…no I don’t own an iPhone yet…sigh) why when he enters his Calendar information on the iPhone it doesn’t show up in his Calendar on his Mac, but when he enters it on his Mac, it’s fine—it syncs to the iPhone with no issues. He wants to be able to enter info into the iPhone remotely and have it sync with his Mac.

He’s got a 17” Macbook Pro with Tiger (latest update) and is actually using .mac still and not MobileMe. I don’t think that this is the problem though.

Yes, he has everything setup properly, password, username and all that has been checked several times. He even removed his account info from both devices and tried to start over. As far as I can tell from reading the official tutorials and such, he is doing everything correctly.