Did you by any chance make a bootdisk. In cases like this they are dang handy. If not you would be well off downloading one of the internet, a good one is Tomsrbt at (I think) www.tomsrbt.net
You might be able to issue 'mount -o remount -w /dev/???' but it probably won't work because your root fs is buisy.
/dev/sda4 /mnt/zip250.0 vfat noauto,user 00
looks a little better like this:
/dev/sda4 /mnt/zip250.0 vfat noauto,user 0 0
That might be it.