Massive Mod under construction

[Fyron]

You do not need to reupload the image mod files. Just point people to:
http://imagemodserver.mine.nu/other/MM/SE4/imagemod/
or here while imagemodserver is offline:
http://imagemod.spaceempires.net/

If you have a handful of extra images, you can just submit them to the image mod and save people from downloading everything twice.

This will cut a lot of download size out of the mod...

[PTF]

The best compression rate might be achieved by 7-zip:
http://www.7-zip.org

At least this is what I have seen for Morrowind mods. A former 140 MBytes zipped mod has been reduced to about 70-80 MBytes by 7-zip.
The best decompression tool that I could think of is, for all formats:
http://www.zipgenius.it/

[Fyron]

Even if you want to stick with ZIP files, you definitely want to get a professional archiving program (7-zip, Izarc, WinRAR, etc.). Pretty much everything makes far smaller ZIP archives than the XP utility and WinZip. Those are great examples of really poor software.