Windows 7 64 bit LAN jitters with Broadcom NetXtreme 57xx Gigabit Controller

Few days ago I've installed Windows 7 (64 bit) on my laptop Dell D630. This laptop has a "Broadcom NetXtreme 57xx Gigabit Controller" as a LAN interface. The OS installation (an upgrade to Home Premium from XP) went smooth. I had a strange feeling that the Internet is crawling so I made few tests comparing the throughput with other computers that I have on my home network. A simple download tests approve that the network throughput from the LAN interface is much slower (I'm talking about factor of 2 to 4, the throughput jitters between 50 to 80 percent) then what I'm used to and comparing to other computers on my network that have a stable max performance.
I also tried the same tests, but this time I was connected through the Wireless interface on my laptop and surprisingly the bandwidth went back to the levels I'm used to, and was stable on the maximum. I think this is focusing the problem to the compatibility of the "Broadcom NetExtreme 57xx Gigabit Controller" with Widows 7.
I tried to update/reinstall the LAN device driver - Didn't help.

It will be great if Microsoft  or Dell or Broadcom attend this issue, till then I would be glad to be assisted.

Thanks, Avi