aztech dsl605eu block
I think you can use "Packet Filtering Firewall Support", to filter any packet that goes or comes from certain IP, comes from **broken link removed**. You must acces the config web page at the router,the "IP" comes specified in the datasheet, for example in a linksys is 192.168.1.1 and in a belkin is 192.168.2.1.
I don't know if you can set a different speed for each interface.
(I don't know if this specific feature of this modem+router can solve this, but it seems to be the first place to look for. This isn't just a DSL modem, it's a DSL modem plus a router, this last is what gives you the ability of filtering packets)
Regards,
Diego