Notes: To turn on remote desktop on a virtualbox machine on ubuntu, do the following:
1)Power off the virtual machine
2)Go to settings for the virtual machine
3)Set the display settings for the Remote Desktop and choose a port (Don´t use 13389 if you are running NoMachine)
4)Start up the Virtual Machine
5)Using the IP of the main box that is running the virutal machine (don´t use the ip address assigned to the virtualbox!!!!) connect via remote desktop.

Thx a lot!
It works for me on IBM T20 and Lubuntu 11.04
Messages "Power down; System halted" resolved.
Power off; Hibernation as well as Suspend functions work as expected

Thanks working for my Dell XPS M1530
Ubuntu 10.04 32 :)

Thanks a lot dude!. this works in my Pentium 4.