WinXP *must not* see the drive !! As soon as WinXP sees the drive, it is unusable for both the Amiga and WinUAE.
Only WinUAE can see the drive. If you connect an Amiga drive to the PC, run WinUAE and select "Add harddrive". Only the Amiga drive should appear in the list.
If the Amiga drive does not appear on the list, it was formerly formatted for DOS/Windows. There is a command line option for WinUAE which disables the filtering. The option is -disablehardrivesafetycheck. You should be *very* careful with this option. With this option, *all* drives are shown in the list. If you accidentally select you Windows drive, all your data is lost and you can install the entire PC from scatch !!
Bye,
Thomas