Sounds like your Ruby installation is broken. Can you try reinstalling Ruby?
-Jeremy
dont undersatnd what is going on here:
supportfiles yahoo$ vagrant up
/Users/yahoo/wdk/supportfiles/Vagrantfile:6: undefined method `project_directory=' for #<Vagrant::Config::VMConfig:0x1845494> (NoMethodError)
from /opt/local/lib/ruby/gems/1.8/gems/vagrant-0.4.1/lib/vagrant/util/stacked_proc_runner.rb:30:in `call'
from /opt/local/lib/ruby/gems/1.8/gems/vagrant-0.4.1/lib/vagrant/util/stacked_proc_runner.rb:30:in `run_procs!'
from /opt/local/lib/ruby/gems/1.8/gems/vagrant-0.4.1/lib/vagrant/util/stacked_proc_runner.rb:29:in `each'
from /opt/local/lib/ruby/gems/1.8/gems/vagrant-0.4.1/lib/vagrant/util/stacked_proc_runner.rb:29:in `run_procs!'
from /opt/local/lib/ruby/gems/1.8/gems/vagrant-0.4.1/lib/vagrant/config.rb:35:in `execute!'
from /opt/local/lib/ruby/gems/1.8/gems/vagrant-0.4.1/lib/vagrant/environment.rb:205:in `load_config!'
from /opt/local/lib/ruby/gems/1.8/gems/vagrant-0.4.1/lib/vagrant/environment.rb:137:in `load!'
from /opt/local/lib/ruby/gems/1.8/gems/vagrant-0.4.1/lib/vagrant/environment.rb:33:in `load!'
from /opt/local/lib/ruby/gems/1.8/gems/vagrant-0.4.1/lib/vagrant/command.rb:12:in `execute'
from /opt/local/lib/ruby/gems/1.8/gems/vagrant-0.4.1/bin/vagrant:7
from /opt/local/bin/vagrant:19:in `load'
from /opt/local/bin/vagrant:19