Go to the Settings/Hardware section, select the Hard drives tab, click "Add Hard Drive...", now find your harddisk amoung the list given, enable read/write if you are feeling brave, then click "Add hard drive".
If you want to *create* an Amiga partition on non-Amiga formatted HD, then you will need to use a console command when launching WinUAE, as otherwise WinUAE does not show it for safety reasons.
