Differnces between Steam and Regular Client

So, I was wondering if you load up Guild Wars from a Steam account, do you automatically log in? Or do you have to create a account on NcSoft like everyone else?

The client is likely the same, but you might be allowed to use your Steam login to play, so it's most probably just a matter of credentials.

Nope you still have to use your GuildWars log-in. The only difference is that you get the Steam-ingame-UI

With Guild Wars, Steam is not of much use (other than the bargain price for the Trilogy). You can already download the client to multiple computers and log-in on your account on any of them. There is no way to start a GW session without using the GW log-in screen.

Even if you don't buy the game off of Steam, you can run the original client through Steam to get the UI overlay.