Note:Unlocking bootloader is necessary to root this particular phone.If you are unwiling/incapable of unlocking your bootloader then please look elsewhere.
Also, before beginning make sure that you have all the adb and fastboot drivers installed for your device.
The fun part:
Unlock your bootloader:
1. Goto http://www.htcdev.com/ and register yourself
2.Click 'unlock bootloader' on the home page>get started.
3.Choose 'htc desire*' from the drop down list.
4.Follow the steps.
After the unlocking is done , download the vroot application from http://www.mgyun.com/en/getvroot and root your device.