I have used the inventory GUI that comes with the default game, it pauses the game when it is open, but i do not wish this to happen anymore. I want the game to continue as normal, even if the inventory has opened.
You'll need to design your own GUI (for example, gInventory) with an InvWindow control on it. Set it's visibility mode in the editor to "Normal, initially off". And then use gInventory.Visible = true; in the script to turn it on (set it to false to turn it off).