Got the same problem here guys.
Using XP, IE6
Tried downloading and unzipping at different times today, but same problem.
PS I thought I had got round it by copying and pasting the contents of the zip file. I uploaded the files, and when I ran the install script, it tells me I am up to date with RC 1 !
PPS Got round it by opening the zip , and dragging/dropping the files and folders onto my hard drive. Pheww!!