My last edit. I had a few mistakes and finally had some time for a re-write. Seems people are getting it though.
Step 1) download and install the one click apk or get it from the market and install it.
http://dl.dropbox.com/u/8699733/erisone010.apk - VERSION 0.1.0
Step 2) Run one click program, read disclaimer, press button.
Step 3) Turn the phone off and reboot phone into the normal operating system. This must be done for the rooting operation to take place.
Step 4) Turn the phone off and reboot into recovery mode. Do this by turning the phone off and then turning it back on by simultaneously holding the Volume UP and Power Button. This will boot you up into Amon's Android System recovery.
Step 5.) Using Amon's recovery and the trackball to navigate and select, pick the backup/restore option which will do a Nandroid backup of the current ROM on your phone. The backup is placed on your SD card under a folder called nandroid.
Step 6.) Once the backup is complete, press the Volume Down button to return to the main menu.
Note: Skip steps 7, 8 and 9 if you want to install a custom ROM right away.
Step. 7.) Once back at the main menu, pick "Flash Zip from SDCard" and then select rootme.zip that was downloaded with the one click program.
Step 8.) Press the Vol Down button to return to the main menu and select "Reboot System Now"
Step 9.) Once the phone is re-booted, go to settings>applications>development and turn usb debugging on.
Step 9.) Uninstall One Click program
Now you are rooted (still on HTC sense) and will be able to do root-only stuff like install root-only apps, delete bloatware, etc.. But you won't be able to overclock without flashing an overclock kernel patch which is included in most custom ROMS
To install a custom ROM...
Make sure to do a nandroid backup before flashing a custom ROM or doing anything scary / major like remove bloatware (system apps), etc
Step 1.) Download custom ROM to SDCard. Download to the top-level (root directory) of your sdcard. Do not download into a folder or it will not work.
Step 2.) Turn phone off
Step 3.) Reboot into Amons recovery mode. Hold Volume Up and Power Simultaneously.
Step 4.) If instructed by the developer, perform the necessary wipes. 2 wipes may be necessary. Wipe Data / Factory Reset and Wipe Dalvik-cache.
Step 5.) Press Volume Down to return to the main menu and select "Flash Zip from SDcard"
Step 6.) Select the custom ROM *.zip file that you downloaded in Step 1.
Step. 7.) Press Vol Down to go back to the Main Menu then select "Reboot System Now"
Enjoy your new rooted eris.