Speed report is as it should be for my 512k/128k:

2004-06-19 14:29:47 EST: 462 / 113
Your download speed : 473611 bps, or 462 kbps.
A 57.8 KB/sec transfer rate.
Your upload speed : 116140 bps, or 113 kbps.

I restored defaults and am doing your LW dl test, and getting 3 hosts at 3KB/s... see what I mean?

The Firewall in OS X preferences: Sharing is not running.
This seems like a clue to me: when I go to the Monitor panel in LW and select "Enable" to see incoming Searches, I get the popup saying
"Leaf node shielded by an UltraPeer..."
This should not be the case, should it? It didn't used to be the case. By default, I do not have "Function as UltraPeer" disabled.
I know that when I was getting expected DL speeds, I was also functioning as an UltraPeer. I am unable to find what has ruined my DL speed... some combination of:
Upgrading to LW 4.0.5
Upgrading to OS X 10.3.4
Turning on Apple's builtin Firewall
Turning off Apple's builltin Firewall