I don't think you need a router with a modem, as you already have one. You should be able to take the "signal" from the modem and route it through the router. ( excellent grammer eh.)
I think that you should contact belkin on freephone 00800 22355460 ( tech support ) and pick the pre-buy option. You could say you were thinking of buying a belkin wireless router click here
and ask there advise. Give them details of your full setup and what you hope to achive.
In my opinion they are good. If you do eventually decide to buy and run into difficulties, then the belkin free phone tech support will talk you through the setting up.
They are really good.