No don't worry, that's nothing scary. Okay, at least your phone isn't bricked per se, the rom is just fucked and not booting onto the OS. From the recovery you
should be able to flash an official rom (i.e without rooting or anything). Unfortunately I don't know how to do it for a Desire

If you want to venture into doing that, do so at your own risk. It's not particularly dangerous as such, but it can get quite scary (mostly because the startup times take a loooong time and you think everything is dead:/).
http://forum.xda-developers.com/showthread.php?t=695667 is a list of all official shipped Roms. Perhaps if you download the official O2 rom (RUU_Brav

2_UK_1.20.207.1_Radio_32.36.00.28U_4.06 .00.02_2_release_124865.exe) and try to flash it over what you have currently, you could revert back to the previous version?
Again, I honestly don't want you to do anything you're not comfortable with doing...
Edit: Could you check what version of HBoot you have?
To check this, turn off your device, then turn it back on with the 'back' key held. On the second line in green text you will see HBOOT- and then a number.