1) Boot into recovery
2) You say you have RA, so select the option for USB-MS toggle with your phone connected to your computer via USB
3) Download and rename the following file to PC36IMG.zip:
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Make sure you don't accidentally rename it to something like PC36IMG.zip.zip (window, by default, hides extensions).
4) Copy that file to the root of your sd card (you can browse your sd card on your computer at this point.
5) Close the USB-MS toggle mode in recovery, and unplug your phone.
6) Turn the phone off, then boot back into hboot, where it will prompt you flash the pc36img file.
7) Once that finishes, you should have a version of RA that will work for you. You can then flash whatever rom it was you were trying to before. Make sure to wipe data/dalvik/cache, of course.
8) Once you have a bootable rom, you can use ROM manager to reflash CW, if you like, and restore your nandroid backup. Before you do that, though, open a terminal emulator and type "cat /proc/mtd" without quotes. If your erase size is 40000, as I suspect, then that is most definitely why your current RA doesn't work. If you want CW back, do not flash 2.5.0.1 if this is the case.
9) If you want to keep RA, I suggest you flash RA 2.1.1 from ROM manager. Let me know if any of these steps don't work.