|So how about LAN bandwidth? Is there a big difference there?|
You can test by moving a big data file. Archive up about 1 GB of data so it's a single file and then do a transfer to the XP machine and another to the Windows 7 machine and compare the amount of time taken to move the same amount of data. If there's no real difference, then there's nothing wrong with the network interface on the Windows 7 machine.
If however there is a big variance then you need to troubleshoot the NIC (network interface) on the 7 machine. As far as troubleshooting goes, I would start by ensuring you have the newest drivers for your NIC. If the ones you have installed right now aren't the most recent, download and install the more recent ones and test.
If that doesn't do the trick, try resetting your TCP/IP stack.
To reset your TCP/IP stack first o pen a command prompt window (ie: Start >> Run >> type cmd and hit Enter) and perform the following command:
netsh int ip reset c:\resetlog.txt
Note If you do not want to specify a directory path for the log file, use the following command:
netsh int ip reset resetlog.txt
Then reboot the computer.
If none of the above does the trick, you may have to remove the interface from device manager and then reboot and let windows "find" and reinstall the interface.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.