Regardless of what operating system is present on the hard disk you are planning to image, you are in fact booting WinPE, which is based on the 32 bit version of Vista, so needs 32 bit Vista drivers as Ghosti has indicated above.
(You only need Ghost64.exe if you are hot imaging while running Win 7 64 bit.)
While WinPE is running, your hard disk is just a device with a bunch of NTFS sectors which need imaging, so the actual operating system present on the drive is of no consequence.
However, do bear in mind that you may also need to add the appropriate SATA drivers (again vista 32 bit) for your machine, as well as the NIC drivers, should you find that you cannot access the disk once your networking issues are sorted out.