The simplest way to connect them using what you propose is to plug the WAN port of the WGR614 into a LAN port on the DGN2000. What you'll have is a network on the WGR that'll talk through the DGN to the internet. What you won't be able to do (easily at least) is have units on the DGN talk communicate with those on the WGR (you may be able to set up some static routing to allow it). You may have some success getting things on the WGR communicate with things on the DGN, but this isn't always 100% reliable without some tweeking.
Your best bet is, as some have stated, is to get a switch and plug that into one of the LAN ports on the DGN. That way you're simply extending your network and everything plugged into the DGN and new switch should communicate without any issues. 10/100 switches are quite cheap nowdays and easy to find (I've even seen them at Walmart) and will provide you with generally a much better solution. If you decide to later setup media sharing the switch will allow it easily, while the two router solution will be difficult, at best, to set up to work correctly depending on where you connect it.
