Sorry for the wait. I've download the game again and was able to open it with 7-Zip and Winrar without a problem, try unziping the archive with Winrar.
Hey, no worries, it was the weekend, wasn't expecting a quick reply. Thanks for the info, I downloaded and installed Winrar and it extracts the file no problems. 7-Zip still says "Can not open file 'SuperSnake3D_PC.rar' as archive" for me, not that it matters anymore, just FYI in case anyone else has any problems.