Was having problems with VMware Server and everytime I was copying data from my machine to the virtual machine it would be highly unstable and extremely slow.  I later found the way to fix this was to disable a few parameters on the ethernet card.  I added the following to /etc/rc.local:

 ethtool -K eth0 tx off sg off tso off

which fixes the problem after a reboot.  However, just typing this as root will allow you to make the changes without rebooting.  The change in rc.local makes it permanent for each reboot of the system.