Zexbig from XDA Developers forum is successfully able to root HTC Desire HD and install custom recovery image. Once you have your HTC Desire rooted, you can able to install any app on your phone.
For this hack to work, make sure that you have not updated your Desire HD (DHD) to the latest version. If you have updated to the latest version, you will not be able to boot custom HBOOT. If you have upgraded your phone then follow this tutorial to degrade your DHD.
How to root HTC Desire HD
1. Download Paul’s Visionary+ tool and install it on your phone. This tool enables root and removes new HTC protection.
2. Run it and enable Set system r/w after root
3. Click Temproot Now! and wait till it’s finished.
4. Click Attempt Permroot Now!.
5. Your DHD will automatically reboot.
To further test that everything is went fine, download an application “terminal emulator”.
Run it and type su.
If you see sign # it mean’s that everything went fine.
Install HBOOT to get S-Off
6. Install engineering version of HBOOT to get S-Off.
7. Download sfjuocekr DHD script for flashing HBOOT.
8. Unzip it and copy it to your SDCard. Make sure that you have on your SDCard root directory with name DHD and all files inside this directory.
9. Rename DHD-smart folder on your SDCARD to DHD.
10. Run Terminal Emulator.
11. Type su
12. Type sh /sdcard/DHD/check
13. If everything went OK type sh /sdcard/DHD/backup
14. If this also went OK proceed with sh /sdcard/DHD/hboot
This command will install engineering hboot which have S-Off turned off.
Install custom recovery image
15. Download and install ROM Manager app from market on your DHD.
16. Run ROM manager and select first option (Flash ClockWorkMod Recovery).
17. Wait until ROM Manager say’s that installation went successfully.
18. After installation tap in Rom manager option and Reboot into Recovery to test that everything went well.
19. DHD should reboot in clockwork recovery manager.