Vigor 2850n

Hi there, I've got a feeling that what I want to do is easy enough but I'm not 100% confident of setting up this router so before I stuff things up completely I thought I'd ask for advice.

I bought this box to replace a separate router / firewall setup which was quite old and fragile. The firewall (Smoothwall) was linux-based and quite easy to configure - it took over an old pc into which I installed three network cards. One to attach to the outside world, one to attach to a dmz, and one to attach to the lan.

So having bought the 2850 I wish to basically recreate this structure. Obviously the router itself is connected to the wan. I've got the "LAN" switch connected to Port 1 (LAN1) on the router, and I've got the "DMZ" switch connected to Port 2 (LAN2) of the router. Computers on the LAN can see the outside world, computers in the DMZ can see the outside world. All good so far.

The next step is to allow computers in the LAN to see computers in the DMZ, but not vice-versa. Any advice on how?

Many thanks,
Pete