COD 4 accounts?

[Kmodo]

How do the COD 4 accounts work on PC?

Are they linked to a cd key? Do you sign in?

I will be playing COD 4 on my PC at home but am wondering if I would ever be able to use account that I rank up else where?

Will I be able to use it at e.g. a Lan centre or my mates house?

thanks

 

[Kmodo]

So in theory could you just copy and paste those files on a memory stick and take them around with you?