System Name/set Up Question, first day with my mac... :) Options

[moonmandala]

so i bought a new ibook. it arrived yesterday and i've never used a mac.
when going through the set up process i didn't realize that what i listed as my 'short name' would show up as my main account/admin and now i can't seem to find out how to change it. i go into the address book and it shows my name and all info that i can change but the 'short name' field is greyed out...then i searched around in the setup files but couldn't seem to find it. does anyone know if i can do this??? or do i just have to live with the stupid name i put in?
thanks!

and oh yeah i don't know how to use this OS yet but it looks like it's gonna be a fun learning process