You should have your phone connected by USB to your PC through this.
Press the "back" button 5 times to make sure you are out of any menus.
Press and hold voice command (button above camera) until you hear a beep.
Say very clearly "Application Settings"
You'll hear 2 beeps.
There will be a prompt on your screen asking if you want to open "Application Settings" It will have two choices [OK] and [Cancel]
To select OK locate the point about 1" from bottom left of screen, anywhere on the left half of screen should be fine. The width of the OK button is half the screen.
Now make sure you phone is oriented in *Landscape* mode.
There will be 4 options
Unknown sources
Manage applications
Running services
Development
Development is what you want. It is located at the bottom of the Landscape screen. Just about 1/8" to 1/4" from the bottom edge (in landscape mode, the bottom edge is actually the side of the phone). Press anywhere in that area, the option spans the entire width of the phone.
Now you will be on the Development page. It will have 3 options. The page will have status bar at the top, then a line with the name of the category "Development" then the 3 options.
USB debugging
Stay awake
Allow mock locations
USB debugging is the one you want. It is about 1/2" from the top of the screen (in landscape mode, top edge is side edge of phone). Press USB debugging.
There will be a confirmation prompt "Allow USB debugging?" with OK and Cancel as options. In landscape mode the buttons each take up half the screen. OK is on the left half of the screen about 1/4" from the bottom edge (in landscape bottom edge is side edge)
If you are successful, you should hear a bunch of USB sounds on your PC and notification sounds on your phone.
If not, press "back" button 5 times to get out of any menus and start again.