Problem in postgresql installation

Hi

I have installed a 7.1.3 postgresql version on my linux server.
When I type "createuser xxxxxxxx" it asks me : Shall the new user allowed to create databases (y/n)?
Shall the new user allowed to create more new user (y/n)?

I answer yes to the both questions and then a bug report said : " psql : connetDbstart() -- connect() failed - no such file or directory
Is the postmaster running locally and accepting connections on Unix socket :'/tmp/.s.PSQL.5432'
createuser : creation of user 'xxxxxxx' failed.

Thanks for your help.
Mr Paquin