can you log-in into the dashboard?
'usually' when you create a wordpress installation, you have to provide an email address, where wordpress will send a password to, which you need to use to log in for the first time - under the username 'admin'. this first user gets all full administrator rights.
what did you do differently?
if you remember the email you provided, try to login as 'admin' and click 'lost your password?'
as described in the above link, you can ftp all theme files - get them from the server, edit them locally on your computer (using something like notepad) and ftp them up to the same location. i do this all the time.
this way you can edit theme files without logging into your wordpress installation.