rails not finding itself?

[Felix Schäfer]

Hello,

I have some trouble getting rails to work: It used to work, but now it  
fails with the following error:
"""
sahaquiel:~ felix$ rails -v
/opt/local/lib/ruby/vendor_ruby/1.8/rubygems.rb:636:in  
`report_activate_error': Could not find RubyGem rails (>= 0)  
(Gem::LoadError)
	from /opt/local/lib/ruby/vendor_ruby/1.8/rubygems.rb:141:in `activate'
	from /opt/local/lib/ruby/vendor_ruby/1.8/rubygems.rb:49:in `gem'
	from /opt/local/bin/rails:18
"""

I installed everything with 'port install rb-rails', and port is  
uptodate. Here are a few details on the system:
"""
sahaquiel:~ felix$ uname -a
Darwin sahaquiel.lan 9.6.0 Darwin Kernel Version 9.6.0: Mon Nov 24  
17:37:00 PST 2008; root:xnu-1228.9.59~1/RELEASE_I386 i386
sahaquiel:~ felix$ sw_vers
ProductName:	Mac OS X
ProductVersion:	10.5.6
BuildVersion:	9G55
sahaquiel:~ felix$ echo $PATH
/opt/local/bin:/opt/local/sbin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/ 
local/bin:/usr/X11/bin
sahaquiel:~ felix$ ruby -v
ruby 1.8.7 (2008-08-11 patchlevel 72) [i686-darwin9]
sahaquiel:~ felix$ ruby -e 'puts $:'
/opt/local/lib/ruby/site_ruby/1.8
/opt/local/lib/ruby/site_ruby/1.8/i686-darwin9
/opt/local/lib/ruby/site_ruby
/opt/local/lib/ruby/vendor_ruby/1.8
/opt/local/lib/ruby/vendor_ruby/1.8/i686-darwin9
/opt/local/lib/ruby/vendor_ruby
/opt/local/lib/ruby/1.8
/opt/local/lib/ruby/1.8/i686-darwin9
.
sahaquiel:~ felix$ gem env
RubyGems Environment:
  - RUBYGEMS VERSION: 1.3.1
  - RUBY VERSION: 1.8.7 (2008-08-11 patchlevel 72) [i686-darwin9]
  - INSTALLATION DIRECTORY: /opt/local/lib/ruby/gems/1.8
  - RUBY EXECUTABLE: /opt/local/bin/ruby
  - EXECUTABLE DIRECTORY: /opt/local/bin
  - RUBYGEMS PLATFORMS:
    - ruby
    - x86-darwin-9
  - GEM PATHS:
     - /opt/local/lib/ruby/gems/1.8
     - /Users/felix/.gem/ruby/1.8
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :benchmark => false
     - :backtrace => false
     - :bulk_threshold => 1000
  - REMOTE SOURCES:
     - http://gems.rubyforge.org/
"""

I'm quite new to ruby and rails, so I have no clue where rubygems  
would look for installed gems, but I assumed that they should find  
each other if all installed with port.

Thanks for the help,

Felix