I have only one computer at home, we can not test file sharing.From your description, the card seems to work in 10M mode.Check your card's Speed LED, if lit? Or else set the media type to 100 M, full-duplex mode.
Reader02 I can help you test for file sharing and upload issues if you want. I have 2 P5GC-MX 1333s that are networked together running Iatkos 5i 10.5.6. And of course both mobos have the attansic chip onboard. Pm me your email address and any specific instructions for testing your kext file, I will reply to you directly.