Newbie Stupid Question

Hi All
I have just installed PostgreSQL on my duel booted Windows 98/Red Hat Linux
system.  I just want to experiment/learn/play with the db without interfering with
real dbs so I'm not connected to anything.  No surprise when I get the error with
the first createdb at the end of the installation, which states:

   Is the server running locally and accepting
   connections on Unix domain socket
   "tmp/.S.PGSQL.5432"?
   createdb: database creation failed

Can anyone help, I'm almost done!
Peace,
Marsie