How to set up a belkin modem/router with time capsule

Need some help please.

I currently have a Belkin ADSL Modem with built in Wireless G Router (model F5D7632)connected to TalkTalk as my internet provider.
I use wireless facility to connect my laptop to modem/router.

I have just bought a new IMac and Time Capsule for Christmas and am having difficulty in understanding how to set up my exisiting Modem/Router for use with the Time Capsule. I understand that I should take an ethernet cable from one of the ethernet ports on the Belkin router and connect it to the WAN port on the Time Capsule, but how do I configure them. I don't understand which device will handle DHCP handing out ip addresses. Both devices aso have a firewall, which one should I use?

I was intending to disable the wireless G network provided by the Belkin Modem/Router and just use the wireless N network from the Time Capsule. Reading several posts on this forum it seems like some people run a G and N network simultaneously. Can this be easily set up and how?

I am trying to make use of my Belkin Modem/Router to save money but if the set up would be made a lot easier I am prepared to buy a stand alone modem (without router) like the Linksys AM200 and connect the Time Capsule to it.

Has anyone encountered a similar setup? please help

Thanks.