Folks at DFT have done it again. These guys have brought USB host capability to the HD2. Current solution adds HID (human interface devices) profile that allows you to connect hard disk drive and flash drives. To connect some USB peripherals, you may need a special cable or a self powered USB hub.
One major requirement is that you should be running Windows Mobile 6.5 on the HD2. Installation is simple. Just get the cab from here and put it on your device via Active Sync and tap on it in the file explorer. Soft reset.
1. Programs -> USBH Switch
2. Disconnect from PC.
3. Press "Switch to Host" button.
4. Connect host device.
5. After some time it should be detected.
6. You can try to use it.
7. After usage you need reset your device to go back USB client mode.
[download cab from here]