If you have an Nforce3 board and are using the build in LAN, this should (hopefully) fix your problem:
1: Goto "Start" > "Control Panel".
2: Double click to open "Network Connections".
3: Right click on your network adapter and go to properties (should be labeled as "NVIDIA nForce Ethernet Controller").
4: Click on "Configure" and go to the "Advanced" tab.
5: Select "Checksum Offload" and choose disable in the window to the right.
6: Click on Ok.
I don't know if this works on other Nforce MB's or not, but it DID finally let my Qwix transfer ISO's again. It also let my remote access program connect again which had stopped working when I upgraded to the Athlon 64. Hopefully this will help a few others out there fix theie problems.
If this has already been discussed, I apoligize. I'm too lazy to search at the moment...