I have scrounged up some info and finally compiled a guide for ESR + FMCB from the PS2 browser. Most of the guide is put together from bits and pieces floating on the Net, but I have updated it with new files and ideas. Tell me if it works! (I have no need, I can just press square from uLE for ESR... :P)
First go into the DVDPLx folder, and grab your region's file. Ex: I own a NTSC U/C console in the US so I would pick DVDPLU.
Next rename your DVDPLx file to DVDELF.bin (matching case IS NECESSARY!)
Now place that file in a usb memory drive.
Copy over the BOOT.elf and FCMB.elf files IN THE SAME DIRECTORY! VERY IMPORTANT, because Free MCBoot will look for DVDELF.bin and BOOT.elf in the same folder it's in while installing.
Then, load up a recent version of uLaunchELF from an already exploited PS2, and once ULE is loaded, take out his memory card and put yours in Slot 1. Make sure there isn't another memory card in Slot 2. Now fire up FCMB.elf, the Free MCBoot installer. Press Select to format (ERASE) your card, if you need to (like corrupt data). Now either press X or Square, it does make a difference: See here:
Press X if your PS2 and the PS2 you are installing from has the same SCPH model number, such as you are installing from a SCPH-39001, and your PS2 is a SCPH-39001. If you're not sure, just press Square.
Press Square if your PS2 and the PS2 you are installing from differs in model numbers, such as your are installing from a SCPH-50001/n and your PS2 is a SCPH-79001. This will make your memory card also compatible with all PS2 versions, as it cross links to get all-version compatibility. Also, if you're not so sure about anything, go ahead and press square, it will result in better compatibility.
After you press X or Square, Free MCBoot will look around for a DVDELF.bin, and BOOT.elf. It will automatically install those. When the installer is done, press Triangle or shut down the PS2. Now swap the memorycards around so the exploited PS2 will boot like normal. Load ULE. Now you can delete the FCMB.elf and the DVDELF.bin safely from your USB drive.
Plug in your memory card in Slot 2, and navigate to it (mc1). You should see a three new folders, called FCMB-CNF, BOOT, and BxEXEC-SYSTEM. The x refers to your region.
Now, go into BxEXEC-SYSTEM. Copy the osdmain.elf file to your USB drive, and on your computer, copy it into the BxEXEC-DVDPLAYER folder you downloaded. Rename that to dvdplayer.elf
Finally, copy over the BxEXEC-DVDPLAYER folder on the memorycard with Free MCBoot installed. Pop in a ESR patched DVD game, and restart the PS2 with the memorycard in Slot 1. The game should load after some pretty colors.
aar36095 for the guide
ffgriever for BOOT.elf (ESR 9a)
jimmikaelkael, neme, coolan, and many others for Free MCBoot 1.5
The many, many nice people at PSX-Scene for hosting all our files
You for reading and exploiting the very powerful Sony PlayStation 2 system!