Definitely not a percentage. I run WinXP quite happily on an 7.4GB drive with room to spare. I recieved this error with 1.8GB free space. That’s 24% free space. I disabled hibernation to boost free space to over 3GB and it installed fine. Re-enabling hibernation still left me with 1.3GB free. So… it only needed .5GB with the options I chose but still demanded 2GB+ (possibly 3GB?) before installing?
Wow. Hard-coded to require 4-6x the drive space it would actually use. I thought Windows was bad…