You're welcome, glad to do it.
The DOS prompt / Command Prompt, is located by clicking the start orb, then all programs, then accessories, you should see it there. You have a choice to just click it and it will open, or else, and some instances it's required, right clicking it and choosing "Run as Administrator". So if you are attempting to perform a task from the command prompt and receive a message, something to the effect, "Requires Elevated Priviledges" then that's when you need to relaunch it using the RunAs feature.
As far as the username and pass word is concerned these can usually be viewed, added, edited using the users option in the control panel. Again, start orb, select control panel, near the top right hand corner you will see a link called "view by" change it to "small icons" then you should see (their in alphabetical order) something called "User Accounts" there you will see links to change password, change account name, manage another account, etc.
Hope this helps.