You need to Mount the disk as a NETWORK drive in the XP Virtual machine
for example if your Windows 7 computer host name is HORSE then say the new HDD on Windows 7 is volume F:
Then you need to connect network drive \\HORSE\F
on the XP VM. (Or if you know the IP address when the HOSTNAME resolution fails to connect then try for example \\192.XX.XX.XX\F
or whatever the Ip address is).
You might need to enable the correct Network setting on the VM system -- NAT usually works otherwise try Bridged or "Host only" networking -- these settings are usually found in thge Virtual Machine configuration files.
Ensure also you can PING the Host machine from the VM and also ping the VM from the Host.
Ensure that the drive is visible and formatted on the Host Windows 7 system first.
Note also that you must have also enabled the Host drive to be SHARED so it can be seen on your network (a single VM running on an independent stand alone laptop is still a "Network" even if your host machine isn't actually connected to the Internet or a router).
(Finally sometimes you need to set a user password since I think with some of the latest security updates Windows is getting fussy about user accounts without a password -- you can still set the login to bypass the initial screen even with a password if you want to).