dropped packets

Can anyone suggest what might be causing this perplexing network
problem?

Short version:

A machine on my home network (gigabit ethernet) drops lots of packets
when receiving at a rate of about 30MB/S or higher. CPU utilization
remains low. Typical output from ifconfig after a netcat session:

eth0 Link encap:Ethernet HWaddr 00:08:54:35:3A:91
inet addr:192.168.254.77 Bcast:192.168.254.254
Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:11585485 errors:0 dropped:206622 overruns:0
frame:0
TX packets:2567897 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:747011954 (712.4 MiB) TX bytes:1482613312 (1.3 GiB)
Interrupt:12 Base address:0xf00

The problem is completely unidirectional. I have managed to send data
FROM this host via TCP at over 45 MB/S with no dropped packets.

Details:

The machine is an Athlon 64 3400+, which should be able to receive at
these rates. The NIC is based on the RTL8169 chip (using the r8169
driver). I am running kernel 2.6.11.

I have tried many things to diagnose/fix the problem, with absolutely
no effect.

1) Cable?
The cable works fine when run between another host and my hub.
2) CABLE?
Replacing *all* cables with brand new CAT6 patch cords has no effect.
3) Hub?
I get zero dropped packets when transmitting at high speed between two
different hosts on the same hub. Switching around the ports didn't
help.
4) Gigabit?
I don't have another gigabit hub, but when I run the connection through
a 10/100 hub there are no dropped packets. But then the speed is
lower, and I get the same effect with the gigabit hub and a slower
transfer rate.
5) Send host?
I have tried sending data from two different hosts to the "bad" one,
with the same results.
6) Driver?
I recompiled the kernel with RX polling turned on and turned off. Both
give the same result. I don't have a gigabit NIC based on another
chipset to test.
7) TCP only?
Hitting this host with a lot of UDP packets has approximately the same
effect (tested with netcat).
8) IRQ?
The second NIC has a different IRQ, and the problem happens with both
of them.

Thanks in advance.

-David

Just in case anyone got to this thread by googling for a similar
problem, here's the answer:

The problem went away as soon as I replaced the NIC with a decent one,
an Intel Pro/1000 MT PCI gigabit adapter.

<tirade>
The realtek 8169 is a piece of crap. Lots of people have trouble with
them. They are not very efficient, and they drop packets without
producing buffer overrun errors. Driver authors don't like them, and
the only reason anybody uses them is that they are so damned cheap.
That's why my motherboard had one built-in, and why the standalone NIC
I bought for $10 had one. If you're having trouble with one of these,
do yourself a favor and buy a decent NIC on ebay for $20. You can even
get an Intel Pro/1000 card for that much at Newegg if you don't mind an
OEM card with no box or manuals.
</tirade>