Thanks prolific.coder, I can see the rubygems installed.
# aptitude install ruby build-essential libopenssl-ruby ruby1.8-dev
Reading package lists... Done
Building dependency tree
Reading state information... Done
Initializing package states... Done
Writing extended state information... Done
The following NEW packages will be installed:
libopenssl-ruby libopenssl-ruby1.8{a} ruby1.8-dev
0 packages upgraded, 3 newly installed, 0 to remove and 98 not upgraded.
Need to get 702kB of archives. After unpacking 2200kB will be used.
Do you want to continue? [Y/n/?] y
Writing extended state information... Done
Get:1
http://ph.archive.ubuntu.com intrepid-updates/universe libopenssl-ruby1.8 1.8.7.72-1ubuntu0.2 [121kB]
Get:2
http://ph.archive.ubuntu.com intrepid/universe libopenssl-ruby 4.2 [5008B]
Get:3
http://ph.archive.ubuntu.com intrepid-updates/main ruby1.8-dev 1.8.7.72-1ubuntu0.2 [576kB]
Fetched 702kB in 10s (69.0kB/s)
Selecting previously deselected package libopenssl-ruby1.8.
(Reading database ... 27583 files and directories currently installed.)
Unpacking libopenssl-ruby1.8 (from .../libopenssl-ruby1.8_1.8.7.72-1ubuntu0.2_i386.deb) ...
Selecting previously deselected package libopenssl-ruby.
Unpacking libopenssl-ruby (from .../libopenssl-ruby_4.2_all.deb) ...
Selecting previously deselected package ruby1.8-dev.
Unpacking ruby1.8-dev (from .../ruby1.8-dev_1.8.7.72-1ubuntu0.2_i386.deb) ...
Setting up libopenssl-ruby1.8 (1.8.7.72-1ubuntu0.2) ...
Setting up libopenssl-ruby (4.2) ...
Setting up ruby1.8-dev (1.8.7.72-1ubuntu0.2) ...
Reading package lists... Done
Building dependency tree
Reading state information... Done
Reading extended state information
Initializing package states... Done
Writing extended state information... Done
# gem -v
1.3.5