the 'flash alternate recoveries' option near the bottom remained gray and didn't let me click on it even in the premium version. from what you're saying though it doesn't sound worth it to me anyway. I just uninstalled it. is there anything close to rom manager using SPR?
I have never installed a custom rom but my understanding of if is that you simply install the ROM manually instead of using ROM Manager. That to me means you would flash the ROM by putting it in your SD card by either doing an install from a zip file or the ROM in the Nandroid folder and doing a restore.
I'm not sure exactly, hopefully somebody will explain who has experience but I am quite sure of a couple things. If you do it from your SD card or Nandroid folder do a backup on SPRecovery of your current OS and then do a wipe of both the cache and data. With a backup if you want to proceed from this point you should be fine.