[HTCotta]

Once you flash the recovery, boot into it. That is where you can make a nandroid backup, it's quite easy you'll figure it out quick. Recovery is really amazing, coming from WinMo i really wish we would have had something like recovery, you'll love it trust me. Also change your phone info you've upgraded!

EDIT: Herp derp...I should probably tell you how to flash recovery and boot into it. Regardless of what any of the DIY's say the easiest way to flash recovery and boot into it is to download an app called "ROM Manager" from the market. Open ROM manager and the first option is to flash current recovery. Keep in mind this is all after you've rooted. Click that first option, recovery will flash and then you should select the option to reboot into recovery and just check it out. ROM Manager provides a super easy way to make backups as you can just select to backup and restore from ROM Manager instead of selecting in from within recovery, both are easy, you'll figure it out.