Ok, It works. Here's how I accomplished it, and some of the features you will find in this rom. I used WINXP Pro SP3.
1. Disable (uncheck) "Allow USB" and "Allow Connections to one of the following" (Comm Ports) settings in Active Sync 4.5
2. Double click the EZBOOT.exe and then click the NEXT button (it's in a language that my computer can't read, so just assume the NEXT button is on the LEFT).
3. With the unit off, and the sim inserted, but no storage card, insert the USB cable and hold the joystick to the DOWN position (this is where many get confused, its the down or south direction, toward your body, NOT pressed IN), and press the power button at the same time. You will see it enter bootloader mode, and it says updating on the phone screen.
4. Now click the NEXT button on the EZBOOT program and it will flash your unit.
5. It took about 15 minutes and I was using a UK version O2 XDA Graphite, with the official WM6 O2 rom.
6. You will see red and green bars going left to right on your phone. Don't panic, it's normal.
7. It seems to finish the last bit faster than the rest, and reboots to the normal O2 Welcome screen, and then a NEW ORANGE Windows 2nd screen, then to the setup screen, with all the normal options.
8. The default homescreen is called Sliding Panel, and there is another new one called Sliding Panel Media which adds shortcuts for playing music, and viewing photos. I am sure someone has written a review of WM6.5 so I will leave the other descriptions for other websites.
A few notes:
it uses bootloader Eboot ver:UK_V3.4.0_XB FUU
and it SAYS you will be flashing OS M_V6.1.0_SZT_080320 and
RADIO V3.17.2 P10_2008-03-20 but I ended up with
RADIO V 2.17.2 P9_2007-06-11 so I guess my radio didn't change? No problem, I made sample texts and calls with zero issues.
The threaded text messaging is kinda cool and the sliding shortcut functions of the homescreen is handy...
In Settings/About it reads: Windows Mobile 6.5 Standard CE OS 5.2.23017 (build 23017.5.3.0). I am guessing that a hard reset will change my radio, but I will leave it for now, as it seems to be working ok. Thanks to cubaseda for the rom.