Description of problem: Please take look at bug #715572. The docs: http://docs.fedoraproject.org/en-US/Fedora/15/html/Release_Notes/sect-Release_Notes-Welcome_to_Fedora_15.html#sect-Release_Notes-Hardware_Overview say "Minimum RAM for text-mode: 256 MiB" but with less than 640 MiB the freeze described in bug #715572 happens even in text mode install. So the docs should be updated to correlate with reality (well, I'd rather see the installer fixed not to need that much resources, but it seems unlikely to happen ...)
*** This bug has been marked as a duplicate of bug 699770 ***