vps's tend to share bandwidth as well as cpu, so you'd see a more stable streaming quality, especially with higher user loads, on a dedicated. But you can certainly go with a vps to start, especially if the provider is good.
If your margins support that, sure. I could get dedicated bandwidth at FDC for about double the cost, but with the margin in my business that's not really feasible to double the cost of >4gbit of connectivity, especially since the streaming quality is good enough even with the shared bandwidth segment.
The flash media server do only duplicate every byte and send it to the clients, right? I think than the CPU power of a deticated is not needed, because no encoding.
The problem should be the traffic. on a 100 mbit line i think i can handle only 400 lients @ 320 kbits.
I will start with a VPS. Thanks for your answer.
Flash media server uses a lot of memory for cache. I've installed it on a 256 vps before but only for limited traffic. If you have a lot of traffic you'll need more like 2gig memory and fast drives. The limited disk i/o on a vps is another reason you'd consider a dedi.
Another item you'll want to mention here as we help you decide how to proceed is:
Which software are you using?
I have had a great experience with my enterprise clients using wowza media server. They were very helpful and the software's been great.