Okay, so now I am at the point were I can start flashing at will with my diamond. but be warned this is a procedure as hand cramping as a hardreset.
As ALWAYS, you mess with your phone at your own risk, if you break something more often than not the good folks at ppcgeeks will try to help you, but anything you do is with the understanding that only you are liable for messing with your phone.
first make sure your diamond is unlocked using the stickies.
to do this follow Tobeychris' guide
http://forum.ppcgeeks.com/showthread.php?t=36062
follow this thread step by step for the UNLOCKING YOUR PHONE: section. after that come back here. (if you have already unlocked your phone at a previous time this is not needed unless you performed a re-lock at some point.)
from this point you need to find yourself the rom you want to flash. the rom will be in a file with a .nbh extension. there are numerous posts with custom roms, and you can find them in the upgrades threads or even tobey links to many of them. if when you download the rom its in an exe that means that someone put their rom into a self extraction zip file and you will need to open that exe using either 7zip (free) or winrar (not free) and pull the .nbh file (RUU_SIGNED.nbh) out of it and transfer it to your phone.
okay now you need to get your .nbh file on your root directory of the internal storage. by root directory that means directly on the "/internal storage" and not in a folder.
next rename that file from RUU_SIGNED.nbh to DIAMIMG.nbh (Note: if you rename it after transferring the file to your phone. Windows mobile hides extensions so don’t tack on an extra .nbh EG: RUU_SIGNED to DIAMIMG)
now you need to hold power, volume down, AND the "<-" button (the button just above end call) it is confirmed that the back button is required for flashing from the internal storage.
at this point once you have all of those buttons pressed, you need to do the magical dance to figure out how to press the stylus into the soft reset hole.
(as an alternative you can completely power off the phone, then hold backspace and volume and while holding those press and hold power till the bootloader pops up)
if done correctly, you will be prompted to press the power button to update the phone.
you are also given the option to press the circle button to cancel and not update if you decide at the last second to not flash.
once it reaches 100% it will just sit there so after it completes you will need to either soft reset or pull the battery. I recommend pulling the battery because sometimes certain roms are quirky and just need the harder reset than just pushing the soft reset button. (don't confuse that statement with a hard reset, though after a new flash I usually do that as well out of paranoia but usually is not needed unless you have some problems.)
It has been confirmed by hippity that flashing JUST the radio via this method does not initiate a hard reset so your data should stay in tact, though I recommend backing up anyways just in case.
**Edit**
I did a little more research, and this is called entering "Triggered bootloader mode" as apposed to the normal bootloader mode.
Happy flashing everybody
**extra edit**
I got my Touch pro yesterday, so though I try to check my old guide threads I may forget so first post your question here, then if I dont get back to you (or someone else doesn't answer your question) pm me and ill get back to whomever asap.
** added hippity's confirmation about flashing JUST the radio from the internal memory not initiating a hard reset.