Download from a different mirror
Here is a link to Sabayon mirrors http://www.sabayonlinux.org/mirrors
The iso image is 1.8 gigabyte and is not a zip file and don't forget to check the md5 before burning
Or you could try the Italian mirror (I downloaded the 32bit version of sabayon 4.2 kde from here) http://na.mirror.garr.it/mirrors/sabayonlinux/
Desktop ASUS M2N-MX SE Plus, AMD 64 X2 Dual Core 5200, 4 Gb RAM, GeForce 9500 1GB
Notebook HP CQ61-311AX, AMD CPU M320, 4 Gb RAM, Radeon HD 4300 512 MB
Wireless AR9285, Audio ATI SBx00 (IDT 92hd75B2x5)
Some mistakes are too much fun to only make once!