New modem, some devices won't connect to old wifi

So I got new services from comcast and they sent me a new modem. I had an old motorolla modem that had no built in wifi, so I use a linksys wireless-N EA2700 router. The new comcast modem comes with a built in wireless router, but I still want to use the old one. So I can't find any helpful identification for the old modem, but I know that the new one with it's own router is an Arris (TG862).

Connected to the internet are:

My laptop, an old thinkpad running Ubuntu (just bought it used from Free Geek two days ago) XFCE (?)
Iphone 4

Unable to connect to the internet are:

Samsung GS3
Dell XPS (running Vista)

I'm a homeowner with a number of roommates and so up to 6 people can be using the internet at a time so I'd like to keep using my dual band router- it's just better than the new comcast one. Everything connected fine to my linksys router before the equipment upgrade. My roommates Vista laptop tells me it can't connect to the DNS server as though it's an ISP issue. Disconnecting some devices to the internet doesn't allow others to connect.

Thanks everyone for taking the time to help me out.
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