The router will require various bits of info and this will vary. Obviously, the minimum is your ADSL service's username and password, but you will also need to know the connection protocol at the very least. This is usally PPP over ATM (PPPoA). Others that you may or may not need include the recommended MTU figure (usually around 1400), the VCI figure and the VPI figure.
It is not essential for you to know the significance of thses figures and terms, and it would take too long to explain them here. They are technical terms and so are difficult to explain simply; but one call or email to Wanadoo should furnish you with all these if you do not already have a record of them from the time of your signup to its service.
I cannot comment on how many of these settings will be inputted manually into a Netgear and which ones will be auto-assigned. A Belkin, for example, simply requires the first three and the other three are optionally adjustable only if needed.