Today I put a few rules in place to prioritize the packets going
to/from my VoIP box.  They work well at ensuring clear calls, but I've
noticed that since adding the rules, the rest of my network traffic
has seemed to get quite a bit slower.  I'm running the cdrom image of
m0n0-1.2 on a 400 MHz PC with 512 mb RAM.  Here's my current ruleset:

http://andersonfam.org/gallery2/d/13628-1/traf_shape.jpg

I tried to take a simpler-is-better approach with one set of rules to
match the up/down VoIP traffic (dumped into a high-priority queue) and
one set to match everything else (dumped into a low priority queue). 
My understanding was that the shaping would only really affect things
when there was VoIP traffic and that if there was no call going on,
traffic would flow as freely (minus a bit of CPU overhead) as before
the rules were put in place.  I guessing that this assumption was
wrong.  I've watched the CPU graph while browsing websites, and it
never gets above 2% or so, so the processing overhead isn't causing
the delay.

Would anyone have a recommendation or two for rules I could add here
to retain the high-priority VoIP traffic, while improving the overall
response time of other network traffic?

Thanks!
-Erik