Make sure you are using the latest driver, version 10.0.6.0 dated 06/12/2009. If not, you can find them in the latest Ethernet driver downloads:
Because the network connections are built into the computer, you might need to check with the system manufacturer for updated BIOS or assistance and to find out if they support your computer with Windows 7.
After some more testing it appears the problem is exacerbated if the drive target is a DFS location. In other words if mapped drive F and G point to \\server1\workgroup vs drives J and K (which point to \\domain\dfsroot\workgroup) then the dfs mapped drives will always take longer to come up. Again Broadcom chipsets are instantaneous.
You might get better results by changing some of your power management / advanced settings so that the network connection does not lower speed in low power states. You can find information on configuring the settings in Re: 82567LM Gigabit Network Connection Link has been disconnected. I hope this helps.