There are two user-configurable parameters that govern how the keyboard behaves: the 'model' (e.g. "IBM ThinkPad R60/T60/R61/T61", "Generic 104-key PC", "Evdev-managed keyboard", and so on) and the 'layout' (e.g. "USA", "United Kingdom", "Brazil", "Spain", "Afghanistan", and so on).
Even though I have a laptop with an 87-key keyboard localised for the UK (e.g. the symbol above the key with the number "3" on it has the UK currency pound symbol "£" instead of the US "#" symbol), I have configured the OS for a keyboard model of "Evdev-managed keyboard" and a keyboard layout of "United Kingdom" (well, actually I have configured three user-switchable keyboard layouts: "United Kingdom", "Brazil" and "Spain"). This would translate to an X.Org command of setxkbmap -model evdev -layout gb,br,es.
I don't have access to a Linux PC with GNOME here in the office, but you should be able to use the GNOME system settings to configure your keyboard model and keyboard layout (i.e. two separate parameters). If the actual i.e. physical layout of your keyboard is a US layout then you can configure the layout as such, but, if it is not already configured as such, try changing the model. Normally this should be configured to be 'Evdev-managed keyboard' because the X.Org evdev generic input driver (x11-drivers/xf86-input-evdev) is used in SL.