newbie

i installed mandrake 10 on my pc, and i choose postgresql as db, i installed
it before in windows, but in linux i dont have idea what happends, i
remebered that i should create an user, but in linux the process is auto and
i when i try to connect by pgadmin i dont know user and password =(

i wrote in user postgre and trusted server but it says

Error connecting to the server: could not connect to server: Connection
refused
    Is the server running on host 127.0.0.1 and accepting
    TCP/IP connections on port 5432?

and the server is up, the service is running,  who can help me please?? =(