virtualbox.org

I installed on a Vista Ultimate 64 Bit machine and created two virtual machines. One to run XP 54 BIT and one to run WIn 7 64 Bit, but when I try to start them I get an error message.

"Failed to start virtual machine Windows XP 64
VT-x is not available(Verr_VMX_NO_VMX).

Undnow error creating(Verr_VMX_NO_VMX)."

Under details, the following infor

Result Code: E_FAIL (0x80004005)
Component: Console
Interface: IConsole {0a51994b-cbc6-4686-94eb-d4e4023280e2}

Does anyone know what the problem is?

Does you PC support hardware-V
Look in the bios and see if you can find VT-x/AMD-v or hardware virtualization.
If you do not have it then 64 bit guests will not work in VirtualBox.