I use a program called Power Archiver, Zhann. It makes Winzip and WinRAR look like MS Paint compared to Photoshop. It operates like .jpg compression, meaning you pick your target filesize and PA will either compress it down to that, or tell you that it's a no-go. Perhaps it might help, but remember that no matter what, you should totally use a zipped version in the final file transfer. If people don't have WinRAR, they can go get it, it's free.