Vista GB LAN Disconnects During Large file Transfer

DETAILED PROBLEM STATEMENT
I keep my personal data folder ("Cliff," ~42GB, many files and subfolders) in the Public Folder on my Desktop PC. In the past (2-3 months ago) I was able to copy this folder across the LAN to the Public folder on my Laptop for those times when I needed to travel with the Laptop.

Now, when I attempt to copy the 42MB folder FROM the Public Folder on my Desktop TO the Public folder on my Laptop, some files/folders get transferred, but the connection fails within 1-5 seconds of initiating the copy. Error 0x80070035 eventually shows up. And, the connection is pitifully slow, ranging from xxKBPS to no higher than 8MBPS.

SOLUTIONS ATTEMPTED
1) Administrative Services-Routing and Remote Access switched from a default of Disabled, to Automatic. Made no difference.
2) Network Magic from Purenetworks/Cisco installed. It helped a little in the sense that more files/folders were copied before the disconnect of the laptop from the LAN. Ultimately not helpful. Now uninstalled.
3) Net Config Server shows Idle Session Time of 15 minutes, the default value. Since my timeouts happen within 1-2 minutes, this would seem to be OK.
4) SpeedGuide TCP/IP Setting for Vista used on Desktop PC (SpeedGuide.net :: TCP Optimizer / Downloads). This appeared to enable me to copy a smaller version (31GB) of the Cliff folder yesterday. But today, cannot copy the remaining 11GB before LAN disconnect.
Thank you for all help!

MORE CONFUSION
Multiple IP Addresses for Desktop PC now appear in Router Interface-
192.168.0.197 Desktop PC with MAC 00:23:54:3b:53:25
192.168.0.198 Desktop PC with MAC 00:23:54:3b:53:25
192.168.0.199 Laptop PC with MAC 00:1b:24:e6:cb:ac
Did Network Magic do this? Is this hurting me? How to undo?

Additional Object in Network Connections Folder-
In addition to Local Area Connection, there is an Incoming Connection object. Did Network Magic create this? It remains after uninstalling Network Magic.
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OS:
Desktop-Vista Home Premium 32-bit.
Laptop-Vista Ultimate 64-bit.

Hardware:
Both PCs are HP with Realtek RTL8168C(P) GB NIC on motherboard.
Router is D-Link DIR-655 with 4 GB LAN ports.

Network Configuration:
-Network Type set to PRIVATE.
-Both PCs are in the workgroup named WORKGROUP.
-Network Discovery is ON.
-File Sharing is ON.
-Public Folder sharing with password is ON. Both PCs (the only PCs on the LAN) have the same username and password.
-Printer Sharing with password is ON.
-Password protected sharing is ON.
-Media Sharing is OFF.

Error Messages:
It always starts by "hanging" on a particular file - but not necessarily the same file each time.
First messages will say something like, "cannot find pathname.filename."
I can select "Try Again" or "Skip."
Next message will say something like "pathname.filename no longer located at pathname.filename."
Eventually, after a message saying the laptop can no longer be located and selecting "Diagnose," I get "Error 0x80070035." The laptop is no longer connected to the LAN.

File transfer achieved after setting Receive Window Autotune to Disabled on the Desktop PC that was the source of the files. The tutorial was very helpful.

File transfer speed for this Gigabit network still very disappointing at only 4-5 MBPS.

Did not try Restricted or High settings due to time consuming nature of large file transfer.

Setting Receive Window Autotune to Disabled on the Laptop PC that was the destination of the files helped very slightly.

Any suggestions for increasing LAN speed would be much appreciated.

Still wondering about Multiple IP Addresses for Desktop PC and Additional Object in Network Connections Folder.