ALTQ in firewall

Hi,

Our house has a shared internet connection (4M/512k ADSL) and the firewall is 
running NetBSD 3.1.1. Currently we are using the built-in IPF to perform all 
filtering. We have one public address for the external interface and 64 public 
addresses for the internal network.

Now, from time to time, some users overload our uplink by sending e.g. large 
amount of digital photos to photo labs and this of course has negative effect 
for all our users as the TCP traffic slows down even though our downlink is not 
congested.

I'm aware that PF supports ALTQ in NetBSD 4.0 but that would mean upgrade and 
I'd rather not upgrade because everything is very stable.

So, is anyone using IPF with ALTQ in NetBSD 3.x? What queueing discipline should 
I use in this case? All real-life examples are welcome...

Martti