I have only come across one way of achieving this, that is, to
install the paid version of DD-WRT, a third-party firmware, into a
router which is compatible with it, namely Linksys' WRT54GL. Their
online store is currently down, but I have checked it out a few
weeks ago and it's 20 Euros (around 40 SGD) if I remember
correctly.
In July 2006, DD-WRT Shop started offering a pay-only "special
version" of the router firmware.[1] It includes increased
functionality such as per-user bandwidth control. Since
then, DD-WRT has been accused of violating the GPL provision
against binary-only public distribution of derivative
works.[2][unreliable source?][3]
- Wikipedia
More info:
http://en.wikipedia.org/wiki/WRT54G#WRT54GL
http://en.wikipedia.org/wiki/DD-WRT
Edit:
Errr ok nvm. I just did some Googling out of curiosity and there is
one free tool that allows bandwidth control through router firewall
configuration.
http://dslreports.com/forum/remark,17099052