HTC Desire Roms Problems

[Scooby Ian]

Hi

I have taken the step to root my desire handset using Unrevoked3 but have now come to the start of my problems.
I have downloaded many roms and tried to load them to the phone using the step by step methods posted with each rom, the phone fails to load any of the new roms I have downloaded and is dissplaying the following messages each time:
E:signature lengh doesn't match Eoco marker
E:signature verification failed
installation aborted
Bad

My phone details are as follows:
Firmware: 2.1-update 1
Kernal: 23.44.00.32u_5.09.0530_2 ~ htc-kernal@and 18-2#1
Build: 1.15.405.4 CL155070 release-keys
HBoot: 0.80.0000
Radio: 5.09.05.30_2

If anyone is able to offer any help it would be most helpfull.

If I wanted to unroot the phone and return it to a stock HTC build can I just install the Android 2.2 software update? I have tried to load a pre Froyo upadate but because the Hboot version on my phone is 0.80 it fails to install because you can't for some reason downgrade the Hboot.
The Froyo update has a Hboot of 0.90 so is it ok to download and install this to return the phone to stock HTC OS?

Sorry if this post isn't in the correct location.
Ian