Ok, I had a few files that had .rom extensions, and that web page said it should be either .v64 or .z64. So I ran that program they had on the site, and it renamed it with the (U)(!) at the end, but the rom itself still has the .rom extension.
Possible file extensions for N64 ROMs are: .n64, .v64, .z64, .rom, .bin, .jap, .usa, .pal and more. The extension is supposed to denote which hardware device was used to dump the ROM, and hence the byte order. However, people are lazy about using the correct extension, so there is no guarantee. A good ROM renaming utility will apply the correct extension for you. The only officially 'correct' file extensions are .v64 and .z64, so I recommend sticking to these, otherwise your emulator might not be able to load your game!
Go there and get "Tool64". Don't be dependent on others for solutions ??? Read the whole page. I'm not tring to be mean, but most new ppl don't seem to try to find the solution for themselfs. Many want to be spoon fed the awnsers and it's annoying.