You have not indicated whether your Ghost boot CD is booting PCDOS or WinPE, although I suspect it is PCDOS as I believe that WinPE came in with GSS 2.5, and also because you refer to autoexec.bat
PCDOS has no native support for USB devices, so you ideally need to use WinPE for your boot environment if you wish to be able to access a USB hard disk using plug and play.
If you want to explore WinPE without first updating to GSS 2.5 then you should have a look at this article:
Adventures with WinPE Symantec Connect
I have used the Ghost executable from Ghost 8.3 with this release of WinPE to backup to USB devices and so you should be able to use the later version in GSS 2 similarly.