Many ways for the latest version (oacs-5-2):

CVS:

cvs -d:pserver:anonymous@cvs.openacs.org:/cvsroot login (press enter for password) cvs -d:pserver:anonymous@cvs.openacs.org:/cvsroot checkout -r oacs-5-2 acs-core

A single package, just use the same command with the package-key name, i.e. forums: cvs -d:pserver:anonymous@cvs.openacs.org:/cvsroot checkout -r oacs-5-2 forums

More info here: http://openacs.org/doc/openacs-5-1/using-cvs-with-openacs.html

Or get the latest DISTRIBUTION:

http://openacs.org/projects/openacs/download/

Or try the INSTALLERS:

Debian: http://openacs.org/forums/message-view?message_id=350859

Windows: http://openacs.org/forums/message-view?message_id=349832

Or try the TARBALLS dynamically generated at: http://eye.openacs.org/viewrep/OpenACS (look at the bottom)