no dns and double-nat

Hi MacRumors,
I have a problem with my time capsule (TC).The problem is, that always, when I am surfing in the internet, playing video-games online or even, when I am on skype, talking with my mates, my internet crashes. It is a major problem, if I am downloading a movie from itunes.
Okay, I will tell you how this happens:
I am downloading a movie on itunes and when I downloaded maybe about 1 of 3gb, the download stops. So I open my airport program, but the time capsule is showing a green light. So I close the app, wait 5 minutes and open the app again. Suddenly the TC light is orange and my TC tells me, that there are 2 problems. So I check what for problems my TC has got. The two problems are: No DNS and double-nat (hope it's also called so in english, because i am german ). So I wait again 5 minutes and suddenly the problems are gone and I can surf the internet again etc.
This wouldn't be that bad, if these problems would come once a day. But sadly they come at least every hour .
So now I would like to know, if you could help me with my problem because I am getting mad!!!
Here is some extra info: I use my TC as Router and as backup for all my music. Because almost everybody in my family has a computer we have 3 macs, one ps3 (which I often play in the internet) and 2 ipod touch which are also always connected with the internet. So could it be, that there is just to much stuff, that is in the internet?
Well, I hope somebody can help me.
Lukas

Okay, Thanks
But, I connected my TC over a cable with this plug, that comes out of the wall and then I connected it again with this thing, that looks like a router (i guess it is one).
And, how do i set my dns? (sorry I know lots more of computers, then of networks ) And why do these problems come and go? Why don't they stay?
And, what is bridge-mode and what does it do, that helps me?

okay, bridge-mode won't help.
I tried it and i couldn't get into the internet.
Any other hints?

okay, got some more info: I hooked the TC up like this: ADSL -> Modem -> TC! But I think, I didn't put the modem into bridge-mode so that the TC can give every computer his own address. stupidly I don't know how to access the modem now and so I don't know how to put it into bridge-mode.
I tried bridge-mode on my TC but i couldn't access the internet . so maybe this is the information, that you need, to help me .

sounds good, but i have a modem and can only connect to it, if i connect my computer over ethernet with it. but my tc is in the cellar and most of my macs are in the first floor, so I can't connect them with the modem. And here is another thing, that I found out: if the internet crashes, my telephone (which is also connected to the modem) "crashes" as well. That means: Nobody can call me and I can't call anybody . So, bridge-mode is a good idea, but I couldn't access the internet because of the modem.
Does that now mean, that I have to go any buy myself a router, than put my tc into bridge-mode and connect all my computers with the router? Because I can access the internet, but after a while it crashes. Example: All computers are CONNECTED with the internet. 2 of 3 are surfing the web. If I now want to play playstation 3 in the internet, than I can play about 10 minutes and after these 10 minutes I will not be able to access the internet with my ps3 and all the other computers will not be able to access the internet as well + nobody can reach me and I can't reach anybody because also my phone has crashed. So I will wait 10-15 minutes and my internet is back again, even if I didn't do anything .

1. I live in Germany
2. I get my internet service from "Kabel Deutschland" translated: "cable germany"
3. Yes I get my phone service from them too.
4. No, I am not the one who does all the networking. My father keeps all the bills but he is not the "best" when it comes to networking.
5. my modem is made by a company called "thomson" but I don't know which model it is.
Okay, well my fathers idea was it to connect the modem with the TC, so that the modem gives the signal to the TC and the TC makes the signal wireless, because on a modem you have to connect your computer over ethernet with it. But my father wanted, that the TC transfers the signal into a wireless signal, so that everybody in the whole house could connect to the TC without using ethernet. But there was 1 problem. The problem was: My father has a really good hi-fi system in the ground floor. So he thought, that he could copy his whole music from all of his CDs in the best quality to the TC, so that he could sell or through away all of his CDs. So he copied the CDs on the TC and got himself an airport express, which he connected to his hi-fi system. He now had the idea to stream the music from the TC onto his macbook and give the streaming signal to the airport express, so he could listen to his music on the hi-fi system (that was before he upgraded to snow leopard). The problem was, that the music would lag. It would play and stop then it would play again etc.. So, always if the wanted to listen to music he connected is macbook over ethernet with the TC, so that the signal would come without problems to his airport express. But after upgrading to snow leopard. He didn't have to connect himself over ethernet with the TC. Everything worked just fine. But to surf the internet faster he has asked the electrician to put a cable from the TC, which is in the cellar to the room, where the macbook is most, which is the 2nd floor. So the TC has to give out a wireless signal and a signal over ethernet.
P.S.: I told my TC to use one public IP. (airport utilities, then double click on the TC, then internet and then there, where you can select: Bridge-mode.

so what shall i do now exactly?
And, rip CDs on the macbook wouldn't be intelligent, because my father copys the CDs in wav format, and he has more than 1000 CDs so that takes up to much space on the macbook.

Okay guys,
I'll explain this, so that everybody can understand! I have a iMac, my sister has a iMac as well and my father has a macbook. I have 2 ipod touches and a PS3 and my father rips his CDs and puts them onto the TC, because the TC has 1 TB of storage and could we now please come back to my internet problem and not talk about where and how my father has riped his CDs?