Software update downloads 3 files:
1) fnwin80x.fsu is a small 1K file containing the latest version # and a brief description of the changes. This file can be deleted.
2) $$FtpDir.tmp is a small 4K temporary file that can be deleted.
3) fnwin80x.exe is the new update that is downloaded when a newer version is requested. This file is about 1.2M in size. This is the file you would backed up if you want to be able to get to this exact version for some reason in the future. This file can be deleted after the update has been installed.Note, the latest version is always available on the web site.
If you are running software update in test mode, then the file names are fnwin80xt.fsu and fnwin80xt.exe.
These files are overwritten whenever you run software update again so there is really no need to delete any files.
"80" in the file names is for version 8.0. "75" would be in the file names for version 7.5.