Hey
MCMLXXXVIII, unfortunatly the only way to really tell what version xbox you have is to crack it open and then follow the guides on how to check.
The serial match isn't 100% positive - just a guide
The best place to go (main page / forum wise) is :
<a href="http://www.xbox-scene.org" target=blank>xbox scene</a>
And as far as xbox live and soft modding go, it's not really wise, as xbox live is constantly updating your dash board and bios, so soft modding will always knacker it up

, you really have to have a hardware chip that can be switched on/off.
I learned that from experience when I tried to soft mod my bro's xbox and he went on xbox LIVE with it
All he got was the dreaded code 23 page instead of his dash
PC_Arcade is the man to talk to about soft modding, so when he sees this will help ya out
In mean time take a gander at xbox-scene
