method redefined errors from many core ruby libs

I have a Fedora Core 6 system on which I have built ruby 1.8.6 and
rubygems 1.1.1 from source, and installed rails 2.0.2 using rubygems.
When I create a new rails app, I get lots of errors that look like
they're coming from internal ruby libraries. Lots of methods
redefined, as if I have some duplicate code somewhere. I also get
errors when generating a simple model (see below.)

I discovered that I did have duplicate installations of rails-2.0.2
under /usr/local/lib/ruby/ and /usr/lib64/ruby/. So, I uninstalled all
the action* gems and rails, which removed them from /usr/local/, and
then manually removed everything under /usr/lib64/ruby/gems/1.8/gems/.
I then reinstalled rails with "gem install rails --include-
dependencies." Everything went back into /usr/local/lib/ruby. No
obvious errors. Next, I created a new rails app. Whoops! Same errors
as before.

Ideas, please? Also, how can I be sure rails is using the version of
ruby I think it is?

$ rails --version
Rails 2.0.2
$ ruby --version
ruby 1.8.6 (2007-03-13 patchlevel 0) [x86_64-linux]
$ gem --version
1.1.1

$ ls /usr/local/lib/ruby/gems/1.8/gems/
actionmailer-2.0.2 activeresource-2.0.2 cgi_multipart_eof_fix-2.5.0
gem_plugin-0.2.3 mongrel_cluster-1.0.5 net-sftp-1.1.1 rake-0.8.1
actionpack-2.0.2 activesupport-2.0.2 daemons-1.0.10
highline-1.4.0 mysql-2.7 net-ssh-1.1.2
activerecord-2.0.2 capistrano-2.2.0 fastthread-1.0.1
mongrel-1.1.4 needle-1.3.0 rails-2.0.2

$ ls /usr/lib64/ruby/gems/1.8/gems/
$

For all the lovely errors: click me: http://pastie.caboo.se/187859

I have a Fedora Core 6 system on which I have built ruby 1.8.6 and
rubygems 1.1.1 from source, and installed rails 2.0.2 using rubygems.

When you build ruby there is an option to say where it should live
(and I do believe it defaults to /usr/local/lib).
From an irb prompt you can verify this with
require 'rbconfig'
Config::CONFIG

If you actually have multiple ruby binaries, rails should just end up
using whatever is on your PATH first.

Fred