There is a known incompatibility between VMPlayer and the forcedeth driver which causes extremely slow network communications between the host and guest:
VMPlayer Forums thread
There was a workaround where you could install nvnet, disable forcedeth, and add some settings to the nvnet invocation:
However, nvnet no longer seems to be available and now there is no alternative except to install a third-party network card and disable the nVidia LAN.
This seems to be a software issue with the forcedeth driver, as the underlying hardware worked great with nvnet. I am posting this to let nVidia and the user community know about this. It'd be nice to see a fix so I can pull this 3com PCI 10/100 card out of my system.