Ouch, big subject! I have the feeling you are pretty knowledgable on the subject, but just in case:

First of all you have to differenciate between streaming (using RTSP/RTP) and progressive download (using HTTP).

Let's start with the easy one, progressive download. You need an HTTP server (i.e. Apache) and a normal 3GP file (for example generated with QTPro). Normally, the only thing you have to do is put the file on the server and give the address to the browser (http://server/path/file.3gp).

For the second one you need a STREAMING server (Helix or Darwin). It wont work with a web server.
Then, depending on the server, you will need specific 3GP file.
The process of streaming consist in taking each media track (audio and/or video) and split it in small pieces (network packets). This process is called "hinting". It can be pretty complexe because of real time and bandwidth constraints. Hinting can be done "on demand" (Helix server) or "offline" (Darwin). The darwin server does not know how to do this hinting, so the file you provide to the server must have been specifically generated for streaming for it to be usable by Darwin. On the other hand, the Helix server does know how to hint, so you can provide it any 3GP file.

So I would first check that you have the right combination of streaming server / streaming content.

I haven't tried streaming on the N800 yet, but I'm very interested by the idea.

If you need more advices, please feel free to PM me (in French?).