Don't give up, you are on the right track. Make sure that you have the right image. You want the 'NAND-Backup' on this page:
http://www.trisoft.de/en_c1000howto.htmAlso, download the Startup Guide as it has some great information on doing the NAND restore. If you read the directions in the section that accompanies the NAND-Backup and the appropriate piece of the startup guide (pgs 29 and 34) I think you will get it.
For my money, if I was going to use a Sharp ROM, I would stick with Cacko, but that is the great thing about the Z, you can try them all and find the one you like. Good luck.