On booting an Installation of ubuntu on the vspehere 7.x client can sometimes show a black screen instead of the actual GUI of ubunutu. One the possible reasons for this could be a simple setting in the virtual machine. To check if its problem with vm setting try the following.
Power off vm and go to edit settings-> virtual
hardware->video card and select option "auto detect settings" and
un-check box enable 3D support if checked.
Once the setting is changed, power on the virtual machine and you should be able to see the ubuntu gui.