Hello. I think you may be taking a road to nowhere. I have not heard of anyone being successful in flashing a ROM from the SD card, although I have heard of ppl trying. If anything goes wrong with your custom ROM, as long as you can still flash, your WM5 VZW ROM can be found here:
http://www.pcdphones.com/uts_downloads.aspx
With instructions here:
http://support.vzw.com/how_to_use/xv...re_update.html
If you want to backup your modifications, you can use SPB Backup to the storage card. If you just want to backup your PIM info, use PIMBackup to the storage card. You will have to load all your cabs again after the ROM flash.