Traffic shaping for asymmetric Internet connection

[Dave Ockwell-Jenner]

My ISP provides me a very asymmetric cable connection to the Internet.
I have a Solaris 7 system with IP Filter that acts as a
router/firewall/NAT between the Internet and the local network in our
house - effectively sharing the Internet connection between people in
the house.
 
Occasionally, someone fires up a P2P application and the sudden flood of
upload traffic increases the latency for download traffic (I assume as
upload becomes saturated, the ACK's for download traffic don't get out
fast enough).
 
Is there some kind of traffic shaping software (preferably freeware)
that I can use to throttle my upstream traffic and bring things to a
sensible compromise?
 
Kind regards, 
--
Dave Ockwell-Jenner
Solar Nexus Solutions
http://www.solar-nexus.com/