b44.ko driver does not work in Ubuntu 6.06 and Dell laptop

Binary package hint: linux-image-2.6-amd64-xeon

On a 64-bit dell Inspiron 6400, the integrated broadcom BCM4401 Ethernet card does not work - the card is recognized, the driver loaded and the eth1 interface appears , but almost no packet is ever trasmitted. I happen to get some packet passing through the card at times, and only one time ever DHCP completed successfully; even with a manually assigned IP not even arp packets can pass the interface. This has happened with all sorts of known-good network cables, and the interface works perfectly under Windows.

However, carrier is correctly recognized, mii-tool show that autonegotiation has completed.

I've rebooted with a custom-built 2.6.18.6 kernel and the card works perfectly there; the firewall setup is the same (iptables-restore, which I use, either fully succeeds or fully fails). So it is definitely a kernel problem.

Looking into git history, no enormous changes have happened.
I cannot find related commits; 639b421b911bbde1e3fb5ed037a4f8c85a5bffcb mentions a fix which probably affects boxes with more than 1Gb of RAM.

The only commit which seems related is d9e2d185bf01e20339158f77c3fca00b02014912, but it seems it is applied on 2.6.15 and all ubuntu 6.06 kernels.

I do kernel development on UserModeLinux so I can test patches and even do bisection search, but currently I'm too busy and I may be so for a time. Please suggest the best action to take. I'll try if I can rebuild the original package with make-kpkg and with changes only to the b44 driver.

Additional info:
Reproduced on a laptop inspiron 6400, with Core 2 Duo T7200, 2Gb of RAM, linux-image-2.6.15-27-amd64-xeon kernel (and I think with linux-image-2.6.15-26-amd64-xeon).

# lspci
0000:00:00.0 Host bridge: Intel Corporation Mobile Memory Controller Hub (rev 03)
0000:00:01.0 PCI bridge: Intel Corporation Mobile PCI Express Graphics Port (rev 03)
0000:00:1b.0 0403: Intel Corporation 82801G (ICH7 Family) High Definition Audio Controller (rev 01)
0000:00:1c.0 PCI bridge: Intel Corporation 82801G (ICH7 Family) PCI Express Port 1 (rev 01)
0000:00:1c.3 PCI bridge: Intel Corporation 82801G (ICH7 Family) PCI Express Port 4 (rev 01)
0000:00:1d.0 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI #1 (rev 01)
0000:00:1d.1 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI #2 (rev 01)
0000:00:1d.2 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI #3 (rev 01)
0000:00:1d.3 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI #4 (rev 01)
0000:00:1d.7 USB Controller: Intel Corporation 82801G (ICH7 Family) USB2 EHCI Controller (rev 01)
0000:00:1e.0 PCI bridge: Intel Corporation 82801 Mobile PCI Bridge (rev e1)
0000:00:1f.0 ISA bridge: Intel Corporation 82801GBM (ICH7-M) LPC Interface Bridge (rev 01)
0000:00:1f.2 IDE interface: Intel Corporation 82801GBM/GHM (ICH7 Family) Serial ATA Storage Controllers cc=IDE (rev 01)
0000:00:1f.3 SMBus: Intel Corporation 82801G (ICH7 Family) SMBus Controller (rev 01)
0000:01:00.0 VGA compatible controller: ATI Technologies Inc: Unknown device 7149
0000:03:00.0 Ethernet controller: Broadcom Corporation BCM4401-B0 100Base-TX (rev 02)
0000:03:01.0 FireWire (IEEE 1394): Ricoh Co Ltd: Unknown device 0832
0000:03:01.1 0805: Ricoh Co Ltd R5C822 SD/SDIO/MMC/MS/MSPro Host Adapter (rev 19)
0000:03:01.2 System peripheral: Ricoh Co Ltd: Unknown device 0843 (rev 01)
0000:03:01.3 System peripheral: Ricoh Co Ltd R5C592 Memory Stick Bus Host Adapter (rev 0a)
0000:03:01.4 System peripheral: Ricoh Co Ltd xD-Picture Card Controller (rev 05)
0000:0b:00.0 Network controller: Intel Corporation: Unknown device 4222 (rev 02)