I have a rooted Dinc as well.
Too create backup of the stock ROM you must perform a nandroid backup.
Here's how:
1. Turn off Phone
2. Hold down the Power Button and Volumn down Button Simultaneously.
3. When the menu appears use the vol buttons to navigate to "Recovery"
4. Press the power button to select "Recovery."
(You should now be in clockworkmod Recovery. Black screen with either green or orange text.)
5.navigate to "backup and restore" using vol buttons. Then press the trackpad button to select.
6. In the next menu select "Restore" (this may take awhile)
7. When you receive the message Backup complete you are finished. Press the power button to go back through the menus and when your back to the main menu select "reboot system now".
you backup is now made and can be found on your SD card under clockwork mod/backups. (Don't rename these files!)
FYI this is a great website for rooting information for your incredible.
Updated: Root the HTC Droid Incredible - Technology - Jonamerica.com
I'm currently rocking CyanogenMOD 7 ROM. IMO the best non-Sense Rom. You should also try out MIUI, Myns Warm 2.2, Sky Raider Roms
Enjoy!