As far as I am aware, only limited access - just basic stats through the web UI, which can be accessed at
http://192.168.1.1. If you click "Manage advanced settings" and then "TalkTalk Wi-Fi Hub", it should be under "xDSL" somewhere down the page - at least if you're referring to the model based on the Sagemcom FAST 5364.
The username and password should be printed underneath the card with the wireless credentials on.