Unfortunately, the HTC SHIFT does not allow you to access the HDD under Snapvue (Windows Mobile side). But, xda-devs is (always) there to rescue. Here is an easy way of using the HDD in Snapvue.
1 – Download Network Browser
2 – Set hdd/sdcard on Vista as a share
3 – Attach Vista to snapvue using usb tool
4 – Install Network Browser
5 – Start Network Browser
6 – File – Network – Rescan network – yes
7 – Workgroup – Computer – drive – enter username and password
8 – Done