First of all, welcome to the forum, because it's my first post here, even if I was a visitor on speed guide before I didn't decided to register before .

Secondly, keep in mind that although I have a little knowledge when it comes to network connections, I'm still not very good at it and I have almost no practical knowledge, so I'll try to describe everything as clear as I can, but I may be wrong in some cases. Also, mind my imperfect English - It's not my native language ^^.

Now, here's the problem. I am living for a year already in this rented flat and I'm using the shared internet connection here. The connection is split between 6 rooms in the flat, although not all rooms have computers connected to the Internet and on a few rooms (including mine) 2 computers are connected through the switch.
So basically my computer is behind a NAT router, and a switch.

The router itself seems not to be configured at all beside the basic (default?) settings allowing all users to connect. Normally when I'm the only person using the connection, my ping is very good, often below 50ms and pretty much always below 100ms to the European servers. The problem begins when someone starts using internet (probably using up all the upload), then the upload fluctuates from as low as 50ms to 1000ms and more + some of the packets don't arrive at all (timeout).
The same problem exist when I'm connected directly to the router and not the switch, so I don't think switch itself is any problem.

The connection speed isn't great either: 1Mbit download/256kbit upload.

The question is: what can be done to maintain the latency (in online games), even when connection is being used, either by prioritizing the ports used by game (QoS maybe?) or simply reserving the small amount of uploads/downloads speeds for each connected host? I've read about port forwarding and QoS a bit, but nothing helped so far...

Any instructions or clues on what can be done or what is the exact cause of the problem and how can it be remedied, at least temporarily are welcome.