Did you follow the directions at
http://forums.androidcentral.com/ht...26-guide-rooting-phone-hboot-2-18-0001-a.html to unlock your EVO?
Did you download clockworkmod or an alternate recovery such as Amon-RA and install the custom recovery? You must install a custom recovery before you can install a custom ROM.
Once you have installed a custom recovery you can download
Goo.im Downloads - Downloading su-bin-3.0.3.2-efghi-signed.zip, copy the zip file to your phone's sd card, and use the recovery to install the su-bin-3.0.3.2-efghi-signed.zip then install superuser and busybox from the Play store.
To install a custom ROM, download the zip file for the ROM to your computer, copy the ROM zip file to your phone's sd card, boot your phone into recovery by shutting down completely and then holding the volume down and power buttons simultaneously for several seconds, select Recovery, wipe both the cache and Dalvik cache at least two times, then select Install zip from sd card and select the zip file for the ROM you have downloaded. My preferred ROM is MikG 3.11
MikG v3.11 [3/9/2012].
Before flashing any new ROM, perform a nandroid backup and make sure your phone battery is at least 40% charged.