Virtual Server - Microsoft Learning Machines

Hi!!!

I have Windows Vista Enterpriser 64 bits Edition with 4 GB RAM. I Have
installed Visrtual Server R2 64 bits edition and then I´ve installed the
virtual machines of MOC 6451A- Planning, Deploying and Managing Microsoft
System Center Configuration Manager 2007. When Im trying to start a virtual
machine, i received the error "Not enough memory to start virtual machine".
That´s not true, because I´ve got 2,5 GB free. Anybody can help me?

I can´t specify the memory, because virtual server, for Microsoft Learning
Machines is only the engine. When I´ve finished the installing of the microsoft
virtual machines under C:\Program Files\Microsoft Learning\6451\Drives I can
see the *vmc and *vhd files and I have an executable file with name
"LauncherApplication.exe" inside of C:\Program Files\Microsoft
Learning\6451\Data that launch a Window of Microsoft Learning with a little
windows where I can see the name of the diferent machines with two buttons to
click in "Launch" or click on "Reset". I can reset the machines bacause the
machines are only for academic purposes. This is a characteristic of this
virtual machines and this work under my notebook with Windows XP SP3 or SP2
and 2 GB RAM, but not work under my other notebook with Windows Vista and 4
GB RAM. Under Windows XP when I click the "Launch" button to launch one
machine vmrc.exe start and the machine start but in Windows Vista a screen
turn up with the message "Not enough memory to start virtual machine". I
suppose that this is a problem of Windows Vista but I can´t get to find a
solution.