gem install postgres failed

Binary package hint: ruby

I installed ruby from ubuntu ( 6.06 ) packages. Then I installed ruby gems from here:
http://rubyforge.org/frs/?group_id=126

Extract, then run 'sudo ruby setup.rb'

Before this, I already have libpq-dev, postgresql-8.1, postgresql-client-8.1, postgresql-client-common installed.

Then I installed postgres ruby gems:
$ POSTGRES_INCLUDE=/usr/include/postgresql sudo gem install postgres
.......
gcc -shared -L"/usr/lib" -o postgres.so postgres.o -lruby1.8 -lpq -lnsl -lpthread -ldl -lcrypt -lm -lc

make install
make: Nothing to be done for `install'.

make clean
Successfully installed postgres-0.7.1

$ irb
irb(main):001:0> require 'rubygems'
=> true
irb(main):003:0> require 'postgres'
LoadError: no such file to load -- postgres
        from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:27:in `gem_original_require'
        from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:27:in `require'
        from (irb):3

Solution:
$ cd /usr/lib/ruby/gems/1.8/gems/postgres-0.7.1
$ sudo make
$ irb
irb(main):001:0> require 'rubygems'
=> true
irb(main):002:0> require 'postgres'
=> true

I don't have this problem in Suse 10.2. I installed ruby and ruby_gems from Suse packages. Then 'gem install postgres' works nicely. No need to make in postgres directory again.