I haven't gotten the ISO working yet, so I'll go ahead and post the bootable USB thumb drive solution for now.
First, you'll need to have a USB thumb drive that is at least 4GB or larger. This process will completely erase its contents, so be sure to backup anything you might have on it before starting.
Second, you will need Virtual Box with a Linux guest installed on it (I used Lubuntu to write the instructions below, but the process is virtually the same for Ubuntu if you have that as a guest instead). We will be using Linux for the "dd" command used to build the thumb drive. There are Windows programs that could do this as well, but I am more familiar with Linux. You can always delete the guest or completely uninstall Virtual Box when you are finished if you need to save space.
Download the n64gscc.raw
file. I have set up a room on SpiderOak called N64 Utils
where you can find a link to download it.
Once the file has been downloaded, copy it onto your thumb drive. We are going to use the thumb drive initially to transfer the file into the Linux guest machine in VirtualBox (alternately, you could just download the file from inside the guest machine rather than from the host).
Go to your Linux guest machine settings, and add the thumb drive, under the USB section:
Now start up the Linux guest machine. Once it has booted, open the thumb drive folder and drag the n64gscc.raw file onto your desktop. This will take a long time to complete, so be patient.
Next, open up a terminal. In Lubuntu, it is under Accessories->LXTerminal:
Install GParted by entering the following into the terminal:
sudo apt-get install gparted
When GParted finishes installing, launch it. In Lubuntu, it should be under System Tools -> GParted:
In GParted, find your thumb drive in the drop-down selection at the top-right corner. It will typically be listed as /dev/sdb but make sure it is the same for you (you can use the name and/or size to identify it. Note if the letter for your thumb drive is not /dev/sdb (for example /dev/sdc or /dev/sdg). You will need to know this later.
Once you have selected your thumb drive, right-click on the large rectangle that indicates the partition, and choose "Unmount" (note: if Unmount is greyed out, you can skip this step):
Next, right-click on the partition again and select "Delete":
Finally, click the green check mark to apply the changes. It will warn you about loss of data (don't worry -- worst that could happen here is you could erase your Linux guest machine if you have the wrong drive selected, such as /dev/sda)
If your thumb drive has more than one partition (which would appear as multiple partition rectangles instead of just one), repeat the above steps to delete all of them.
Next, open up the terminal again (Accessories->LXTerminal). Enter the following command. NOTE: if you saw in the previous step that your thumb drive was some letter other than /dev/sdb (such as /dev/sdc or /dev/sdg), modify the command to match.
sudo dd if=~/Desktop/n64gscc.raw of=/dev/sdb
The above command will take a very long time to finish, so be patient. When it is complete, shut down the Linux guest machine. Your thumb drive should now be ready to use!OPTIONAL STEPS:
"Checking the thumb drive for errors": show
From your Virtual Box Linux Guest (with thumb drive plugged in), launch GParted (System Tools -> GParted), and select your thumb drive from the dropdown on the top-right (typically /dev/sdb). Check to see if there is a warning icon:
If there is, right-click on the first partition and select "Check". Click on the green check mark icon to apply the changes.
BACK OUT: "Adding space to the thumb drive for everyday use": show
If your thumb drive is larger than 4GB, there will be a lot of wasted space after running the above process. You can make this area available for everyday use (so that your thumb drive doesn't have to be dedicated to only running the N64 utilities).
To do this, launch your Virtual Box Linux Guest (with thumb drive plugged in), run GParted (System Tools -> GParted), and select your thumb drive from the dropdown on the top-right (typically /dev/sdb).
Right-click on the empty unallocated space in the partitions rectangle, and choose "New". For the file system, select "fat32":
Click "Add", then click the green check mark icon to apply the changes.
"Restoring the thumb drive to its original state": show
If you want to completely remove the utilities from your thumb drive and restore it to its original (empty) state, start up your Virtual Box Linux Guest (with thumb drive plugged in). Once it is loaded, launch GParted (System Tools -> GParted), and select your thumb drive from the dropdown on the top-right (typically /dev/sdb). Right click on any partitions and choose "Delete". Click the green check mark icon to apply the changes. The rectangle should now show only empty (unallocated) space.
Then right-click on the empty unallocated space and choose "New". For the file system, choose "fat32":
Click "Add", then click on the green check mark icon to apply the changes.