STEP 1. Open odin (http://www.mediafire.com/download.php?73ta726ghelw381) and place the linked file below in the "PDA" section and WAIT. You will need 7zip or the like to extract the tar image from the zip file below. This particular type of odin file is the only kind that I know of that contains the proper bootloaders to re-partition your phone. ONLY THE PDA SECTION!!!!
Link removed. My dropbox account was suspended due to excessive traffic. I'll figure out another place to upload and then post the link.
STEP 2. Then, place this file in the "PIT" section in odin and WAIT.
http://dl.dropbox.com/u/20070269/atlas_v2.3.pit <---*Atlas_v2.3 Re-partitioning "PIT" file*
STEP 3. And place a check in the "Re-partition" box in odin.
STEP 4. At this point you need to power off your phone. Then, enter download mode by holding the volume down button and continuing to hold it while you plug the cable into your phone, you should then see a yellow "downloading" screen popup. If/when this happens, go to step 5.
STEP 5. When you have done the first 4 STEPS, THEN hit the "START" button in odin and wait about 5-10 minutes until you see the green "PASS" in odin and profit. ***You must allow the phone to boot fully one time after running this odin process so that it can wipe the phone and complete the the re-partitioning.*** However, when the phone boots, you will be on stock, binged, bloated, unrooted TouchWiz. So odin a recovery and remedy that situation quickly!!! And just in case there are any misconceptions, you do NOT need to be rooted to install a custom cwm recovery.tar file with odin. So unless you plan on staying stock, you don't need to root again because any rom you flash will already be rooted. So just odin a recovery and boot immediately into the recovery via the 3 finger method (holding both volume up and down buttons and the power button at the same time and continue to hold them until you see the samsung logo). YOU MUST DO IT THIS WAY BEFORE THE PHONES BOOTS UP NORMALLY OR YOU WILL LOSE THE RECOVERY THAT YOU JUST ODINED! Then, as good practice, follow the instructions of the next paragraph.
And as a good suggestion, if you want voodoo converted partitions (in others words, if you want to flash a voodoo kernel) after odin does it's thing, flash this package (courtesy of navenedrob) from cwm recovery 3x before flashing whatever rom in conjunction with a voodoo kernel you were wanting to flash after coming from CM7 MTD/GB MIUI. Here is the link, flash this if you want voodoo partitions (ext4): http://dl.dropbox.com/u/20070269/ext4_formatter_all.zip . This will help to insure that you obtain a clean install of whatever rom/voodoo kernel you are flashing after coming from CM7 MTD/GB MIUI ***If you flash the Ext4 package, you must flash a voodoo kernel afterwards or you will have another brick.***
It is absolutely mandatory that you follow these steps exactly to properly get off of CM7 MTD/GB MIUI so that you can flash another rom. Attempting another method or not following these steps implicitly will result in eventual problems down the line and/or a bricked phone and you will have to follow this guide to fix it.