System Requirements:

* 32-bit or 64-bit version of Windows 2000, XP, or Vista
* Rhino 4.0
* 100MB of disk space
* 2GB RAM (4-16GB recommended for 64-bit systems and very large models)
installation file:
http://files.na.mcneel.com/Releases/Rhino/5.0/2009-09-17/Beta/rh50beta_x64_en_20090917_1144.msi

http://files.na.mcneel.com/Releases/Rhino/5.0/2009-10-06/Beta/rh50beta_x86_en_20091006_1857.msi

patch 64bit:
http://www.sendspace.com/file/k7j1pg

more information about this release:
http://download.rhino3d.com/rhino/5.0/wip/?show_all=true&rel=3