Rails: OpenID and ImageScience

I’m having trouble sudo installing gems for my applications…

When I:
sudo gem install ruby-openid

I get this error:

“user” is not in the sudoers file. This incident will be reported.

Great… So I try it without the ‘sudo’ and I get this error:
Install required dependency ruby-yadis? [Yn] Y
ERROR: While executing gem … (Errno::EACCES)
Permission denied - /usr/lib/ruby/gems/1.8/cache/ruby-yadis-0.3.4.gem

Same with ImageScience…

Does anyone know how to get around this issue? Thanks