virtualbox.org

Have the current version of VBox installed on XP Pro SP3 and currently am using 32 bit versions of Vista Ultimate and Win7 RC1. However I have tried installing the 64 bit RTM of Win7 Pro and the install fails with the error that the current hard ware does not support a 64bit O/S. CPU is an AMD64 3500 CPU with 2 GB RAM.

ANy idea why this is happening?

Look in the bios and see if the PC supports hardware-v (VT-x/AMD-v). If it does not then you can not run 64 bit guests in VBox.

OK that explains why the problem is occurring. Older machine that does not have that capability. Could of sworn I had the Bets 64bit of Win7 installed on this box earlier this year.