windows to linux internet connection sharing slow
 

I have a 256kbps cable internet connection going into a windows box (unchangeable).

A linux box (arch linux) is connected to the windows machine via crossover cable.

The connection is shared in windows. Linux does get online, but the connection is laggy, the downloads (firefox, curl, wget etc) freeze and so on.

When i swith the linux box to windows (dual boot), the connection is not slow. So its not due to the cabling or anything. Also, I don't think its due to ipv6 ebcause when I disable it in firefox, there is no change.

What to do?

edit:
(diagram)
[modem]--o--[windows]--->[linux(slow internet)/windows(normal internet)]