Setting QoS bits

Anyone know how to set QoS bits on a per-packet basis?

The QoS Packet Scheduler allows you to control bandwidth (via IIS), and can
also control the QoS bits on that traffic as well (via GP). However, I'm
trying to adjust the QoS bits on traffic that doesn't originate from a QoS
compliant piece of software. Ideally, I'd like a program (or a solution)
that takes all the traffic from a particular source and forces the QoS Packet
Scheduler to set the QoS bits. The ipchains firewall (for Linux) has a
similar option in it, but I can't locate anything for Windows that will do
the same.

Any ideas? Thanks!