Also, only reason I purchased linksys because thats whats installed in their other office but they have comcast cable instead of dsl. I would have recommended netgear over linksys.
Bah the WRT is the best thing going. ESPECIALLY when your flash dd-wrt linux (but thats another story)

You got so much **** screwed up there you have to start from day 1. Reset DSL router to factor condition. Hook a PC up to it and record the address it gives you AND the Nameservers. Tracerout www.cisco.com (because cisco makes the kick ass WRT series). Record your trace. This will show you the DSL routers gateway. They had you changing all that **** on the DSL rounter for some reason that does not make sense. Because YOU stated your wireless connections worked fine but the ehternet connection did not. But regardless you now have the DSL modem working on a single pc and you know through trace route and IP assignment it's nameserver, it's gateway and at least one clear path to Cisco.com. Take the same pc configured for DHCP off the DSL router. Now plug your WRT into the designated port on the DSL modem for routers, if there is one, of not just plug it in. OH, reset that WRT to factory default BEFORE you do that. Just hold in that reset button on the back for a few minutes. Connect your PC and let it pull an ip through ethernet. It should come from the WRT. You said it was pulling the "correct" ip from the WRT. That means it is in the upper block of that range meaning X.X.X.100. Verify this. Not sure why the DSL needs to be bridged for simple internet surfing. The DSL should nat it's internal interface and the WRT should nat it again. But if that is not the case you bridge the DSL and NAT the WRT in many cases.

But since this is old and the problem may be resolved I'll stop. But next your would use that pc on ehternet to trace the the name servers your recorded earlier. if they resopond the link from the WRT through the DSL is fine. At least with that single PC. You did hook the PCs to the WRT router right? If you leave them on the DSL then bridge it, no good.