How to limit internet traffic in some computers of my home network?

Sometimes routers have a QoS (Quality of Service) options that might be helpful in this situation. Sorry for not being more specific, but hopefully it might get you better results searching with that term or looking for QoS settings in your router configuration.

use a router that is supported by DD-WRT (the D-Link DIR-655 is not supported)

* supports more than 200 different devices
* comprehensive functionality
* supports all current WLAN standards (802.11a/b/g/n*)
* supports outdoor deployment*
* supports enhanced frequencies *
* VPN integration
* supports various Hotspot systems
* bandwidth management
* multilingual user interface

for the Windows computers, you may use NetLimiter, a nice software solution