I haven't run into the permissions problem (yet) reported here. Using the curl command here I don't think it's necessary to do the staff group thing but am running into other problems. At first I ran into problems because the ruby 1.8.2 in /usr/bin didn't support the RUBY_PATCHLEVEL variable. I downloaded the ruby one-click installer (1.8.6) and moved it to /usr/bin and now I am getting this error when running 'brew install git':
no such file to load -- no brew-install.rb
(I tried installing newer ruby versions first but RVM now requires gcc 4.2 which is not present in the newest Xcode (2.5) that will run on tiger.)