Can't boot from ISO in vSphere

Hi all,

I'm having a problem with a new infrastructure that has just been set up.....  The machine that has the vSphere installed on it is in a remote location to the actual ESX 4 host and there is a VPN  connection between the 2 sites.  I have been able to add the host into the inventory fine, create new VM's fine, but when I come to boot off an ISO image that is on the vCentre machine to install the guest O.S. ( Windows Server ), the VM's are not booting.....?

Is this because the vCentre is in a remote location, or would there be any other reasons for this?

Thanks

Adam