Here are the steps I took to get all this working on my Infuse.
Do a full backup and copy the backup to your computer. Unless you don't care about what's on there now.
Use this to return the phone to stock:
[ODIN][UCKD5] Odin - Stock (100% or Root+3e) - (Update 06/05/11) - xda-developers
Then format the SD cards.
Then root the phone.
Then install "Root Manager" so you can access/copy files around (costs a couple $ but worth it).
Then install ROM Manager.
Then install ROM Manager Premium (also a couple $ but worth it).
Then install Clockwork mod.
Then do the "3E fix" step by step using the video method.
Now you should be able to install the ROM.
If it's the stock AT&T 2.3.5 ROM, then I
recommend against it. Buggy as heck and didn't work at all well for me.
I couldn't get CM7 to work with bluetooth for my car radio but it worked okay otherwise.
MYUI also doesn't work w/bluetooth (last I checked).
I installed Infused V2 ROM and it's been perfect.