I've had a problem with one computer on my network receiving data very slowly (56Kbps). It could send data at full speed (8Mbps), and other computers on the network send and receive at full speed.

After trying everything including deleting/re-adding the adapter, ensuring that only TCP/IP was installed, trying a different NIC, etc., I finally found something that improved the situation, although perhaps not a complete fix.

In the registry under key "HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\VxD\MSTCP" there were two entries that did not occur on a computer established more recently. The entries were "DefaultRcvWindow" and "DefaultTTL". These entries are the ones that you can optimize for better modem/Internet throughput.

The trick here is that the aforementioned Registry key occurs only once per machine, so when you attempt to optimize your TCP/IP Internet connection, you are also going to "optimize" your LAN TCP/IP setting!!

I deleted these entries and went from 56Kbps to 6Mbps. Still not the 8Mbps going the other way, but very much improved!

Now the usual disclaimer -- *** Do Not do this unless you are familiar with editing the Registry by hand. Make a backup of the Registry before making any changes. ***