Just to inform you guys that i tried the USPL Method 3 times and always got an error message UPDATE ERROR (i think it was error number 270 ??).
Well, that was because after the DOS mode went until 100, and the dialog box for the ROM Update Utility appeared, this dialog box ask to wait for the PDA to be activesynced before presing the "UPDATE", so i was waiting for the PDA to reconnect to activesync (while in a black screen mode) before pressing update . THAT was the mistake. Don't wait for it to RE connect to activesync (strange right ?) and just press the NEXT and UPDATE without waiting anything.
THEN it worked i just upgrade to WM6 without VENDOR ID error anymore thanks to the USPL method
HTC Touch HD- ROM 1.14.406.3 (22273) FRE Rom Date: 10/24/08 Radio Version : 1.09.25.14 Protocol Version: 52.49a.25.26U
----- BELOW PDA ARE FOR SALES ----
HTC Kaiser= ROM 1.56.406.5 FR ROM Date : 08/30/07 Radio Version : 184.108.40.206 protocol version : 22.45.88.07H
HTC P3300=ROM 3.7.707.1 WWE Rom date : 6/21/07 Protocol Version : 220.127.116.11 ExtROM: 3.6.707.101